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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
commit2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch)
tree848558de17fb3008cdf4d861b01ac7781903ce39 /Documentation/driver-api/thermal
parentInitial commit. (diff)
downloadlinux-upstream.tar.xz
linux-upstream.zip
Adding upstream version 6.1.76.upstream/6.1.76upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/driver-api/thermal')
-rw-r--r--Documentation/driver-api/thermal/cpu-cooling-api.rst107
-rw-r--r--Documentation/driver-api/thermal/cpu-idle-cooling.rst199
-rw-r--r--Documentation/driver-api/thermal/exynos_thermal.rst90
-rw-r--r--Documentation/driver-api/thermal/exynos_thermal_emulation.rst61
-rw-r--r--Documentation/driver-api/thermal/index.rst20
-rw-r--r--Documentation/driver-api/thermal/intel_dptf.rst272
-rw-r--r--Documentation/driver-api/thermal/intel_powerclamp.rst320
-rw-r--r--Documentation/driver-api/thermal/nouveau_thermal.rst96
-rw-r--r--Documentation/driver-api/thermal/power_allocator.rst281
-rw-r--r--Documentation/driver-api/thermal/sysfs-api.rst535
-rw-r--r--Documentation/driver-api/thermal/x86_pkg_temperature_thermal.rst55
11 files changed, 2036 insertions, 0 deletions
diff --git a/Documentation/driver-api/thermal/cpu-cooling-api.rst b/Documentation/driver-api/thermal/cpu-cooling-api.rst
new file mode 100644
index 000000000..645d914c4
--- /dev/null
+++ b/Documentation/driver-api/thermal/cpu-cooling-api.rst
@@ -0,0 +1,107 @@
+=======================
+CPU cooling APIs How To
+=======================
+
+Written by Amit Daniel Kachhap <amit.kachhap@linaro.org>
+
+Updated: 6 Jan 2015
+
+Copyright (c) 2012 Samsung Electronics Co., Ltd(http://www.samsung.com)
+
+0. Introduction
+===============
+
+The generic cpu cooling(freq clipping) provides registration/unregistration APIs
+to the caller. The binding of the cooling devices to the trip point is left for
+the user. The registration APIs returns the cooling device pointer.
+
+1. cpu cooling APIs
+===================
+
+1.1 cpufreq registration/unregistration APIs
+--------------------------------------------
+
+ ::
+
+ struct thermal_cooling_device
+ *cpufreq_cooling_register(struct cpumask *clip_cpus)
+
+ This interface function registers the cpufreq cooling device with the name
+ "thermal-cpufreq-%x". This api can support multiple instances of cpufreq
+ cooling devices.
+
+ clip_cpus:
+ cpumask of cpus where the frequency constraints will happen.
+
+ ::
+
+ struct thermal_cooling_device
+ *of_cpufreq_cooling_register(struct cpufreq_policy *policy)
+
+ This interface function registers the cpufreq cooling device with
+ the name "thermal-cpufreq-%x" linking it with a device tree node, in
+ order to bind it via the thermal DT code. This api can support multiple
+ instances of cpufreq cooling devices.
+
+ policy:
+ CPUFreq policy.
+
+
+ ::
+
+ void cpufreq_cooling_unregister(struct thermal_cooling_device *cdev)
+
+ This interface function unregisters the "thermal-cpufreq-%x" cooling device.
+
+ cdev: Cooling device pointer which has to be unregistered.
+
+2. Power models
+===============
+
+The power API registration functions provide a simple power model for
+CPUs. The current power is calculated as dynamic power (static power isn't
+supported currently). This power model requires that the operating-points of
+the CPUs are registered using the kernel's opp library and the
+`cpufreq_frequency_table` is assigned to the `struct device` of the
+cpu. If you are using CONFIG_CPUFREQ_DT then the
+`cpufreq_frequency_table` should already be assigned to the cpu
+device.
+
+The dynamic power consumption of a processor depends on many factors.
+For a given processor implementation the primary factors are:
+
+- The time the processor spends running, consuming dynamic power, as
+ compared to the time in idle states where dynamic consumption is
+ negligible. Herein we refer to this as 'utilisation'.
+- The voltage and frequency levels as a result of DVFS. The DVFS
+ level is a dominant factor governing power consumption.
+- In running time the 'execution' behaviour (instruction types, memory
+ access patterns and so forth) causes, in most cases, a second order
+ variation. In pathological cases this variation can be significant,
+ but typically it is of a much lesser impact than the factors above.
+
+A high level dynamic power consumption model may then be represented as::
+
+ Pdyn = f(run) * Voltage^2 * Frequency * Utilisation
+
+f(run) here represents the described execution behaviour and its
+result has a units of Watts/Hz/Volt^2 (this often expressed in
+mW/MHz/uVolt^2)
+
+The detailed behaviour for f(run) could be modelled on-line. However,
+in practice, such an on-line model has dependencies on a number of
+implementation specific processor support and characterisation
+factors. Therefore, in initial implementation that contribution is
+represented as a constant coefficient. This is a simplification
+consistent with the relative contribution to overall power variation.
+
+In this simplified representation our model becomes::
+
+ Pdyn = Capacitance * Voltage^2 * Frequency * Utilisation
+
+Where `capacitance` is a constant that represents an indicative
+running time dynamic power coefficient in fundamental units of
+mW/MHz/uVolt^2. Typical values for mobile CPUs might lie in range
+from 100 to 500. For reference, the approximate values for the SoC in
+ARM's Juno Development Platform are 530 for the Cortex-A57 cluster and
+140 for the Cortex-A53 cluster.
diff --git a/Documentation/driver-api/thermal/cpu-idle-cooling.rst b/Documentation/driver-api/thermal/cpu-idle-cooling.rst
new file mode 100644
index 000000000..c2a7ca676
--- /dev/null
+++ b/Documentation/driver-api/thermal/cpu-idle-cooling.rst
@@ -0,0 +1,199 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+================
+CPU Idle Cooling
+================
+
+Situation:
+----------
+
+Under certain circumstances a SoC can reach a critical temperature
+limit and is unable to stabilize the temperature around a temperature
+control. When the SoC has to stabilize the temperature, the kernel can
+act on a cooling device to mitigate the dissipated power. When the
+critical temperature is reached, a decision must be taken to reduce
+the temperature, that, in turn impacts performance.
+
+Another situation is when the silicon temperature continues to
+increase even after the dynamic leakage is reduced to its minimum by
+clock gating the component. This runaway phenomenon can continue due
+to the static leakage. The only solution is to power down the
+component, thus dropping the dynamic and static leakage that will
+allow the component to cool down.
+
+Last but not least, the system can ask for a specific power budget but
+because of the OPP density, we can only choose an OPP with a power
+budget lower than the requested one and under-utilize the CPU, thus
+losing performance. In other words, one OPP under-utilizes the CPU
+with a power less than the requested power budget and the next OPP
+exceeds the power budget. An intermediate OPP could have been used if
+it were present.
+
+Solutions:
+----------
+
+If we can remove the static and the dynamic leakage for a specific
+duration in a controlled period, the SoC temperature will
+decrease. Acting on the idle state duration or the idle cycle
+injection period, we can mitigate the temperature by modulating the
+power budget.
+
+The Operating Performance Point (OPP) density has a great influence on
+the control precision of cpufreq, however different vendors have a
+plethora of OPP density, and some have large power gap between OPPs,
+that will result in loss of performance during thermal control and
+loss of power in other scenarios.
+
+At a specific OPP, we can assume that injecting idle cycle on all CPUs
+belong to the same cluster, with a duration greater than the cluster
+idle state target residency, we lead to dropping the static and the
+dynamic leakage for this period (modulo the energy needed to enter
+this state). So the sustainable power with idle cycles has a linear
+relation with the OPP’s sustainable power and can be computed with a
+coefficient similar to::
+
+ Power(IdleCycle) = Coef x Power(OPP)
+
+Idle Injection:
+---------------
+
+The base concept of the idle injection is to force the CPU to go to an
+idle state for a specified time each control cycle, it provides
+another way to control CPU power and heat in addition to
+cpufreq. Ideally, if all CPUs belonging to the same cluster, inject
+their idle cycles synchronously, the cluster can reach its power down
+state with a minimum power consumption and reduce the static leakage
+to almost zero. However, these idle cycles injection will add extra
+latencies as the CPUs will have to wakeup from a deep sleep state.
+
+We use a fixed duration of idle injection that gives an acceptable
+performance penalty and a fixed latency. Mitigation can be increased
+or decreased by modulating the duty cycle of the idle injection.
+
+::
+
+ ^
+ |
+ |
+ |------- -------
+ |_______|_______________________|_______|___________
+
+ <------>
+ idle <---------------------->
+ running
+
+ <----------------------------->
+ duty cycle 25%
+
+
+The implementation of the cooling device bases the number of states on
+the duty cycle percentage. When no mitigation is happening the cooling
+device state is zero, meaning the duty cycle is 0%.
+
+When the mitigation begins, depending on the governor's policy, a
+starting state is selected. With a fixed idle duration and the duty
+cycle (aka the cooling device state), the running duration can be
+computed.
+
+The governor will change the cooling device state thus the duty cycle
+and this variation will modulate the cooling effect.
+
+::
+
+ ^
+ |
+ |
+ |------- -------
+ |_______|_______________|_______|___________
+
+ <------>
+ idle <-------------->
+ running
+
+ <--------------------->
+ duty cycle 33%
+
+
+ ^
+ |
+ |
+ |------- -------
+ |_______|_______|_______|___________
+
+ <------>
+ idle <------>
+ running
+
+ <------------->
+ duty cycle 50%
+
+The idle injection duration value must comply with the constraints:
+
+- It is less than or equal to the latency we tolerate when the
+ mitigation begins. It is platform dependent and will depend on the
+ user experience, reactivity vs performance trade off we want. This
+ value should be specified.
+
+- It is greater than the idle state’s target residency we want to go
+ for thermal mitigation, otherwise we end up consuming more energy.
+
+Power considerations
+--------------------
+
+When we reach the thermal trip point, we have to sustain a specified
+power for a specific temperature but at this time we consume::
+
+ Power = Capacitance x Voltage^2 x Frequency x Utilisation
+
+... which is more than the sustainable power (or there is something
+wrong in the system setup). The ‘Capacitance’ and ‘Utilisation’ are a
+fixed value, ‘Voltage’ and the ‘Frequency’ are fixed artificially
+because we don’t want to change the OPP. We can group the
+‘Capacitance’ and the ‘Utilisation’ into a single term which is the
+‘Dynamic Power Coefficient (Cdyn)’ Simplifying the above, we have::
+
+ Pdyn = Cdyn x Voltage^2 x Frequency
+
+The power allocator governor will ask us somehow to reduce our power
+in order to target the sustainable power defined in the device
+tree. So with the idle injection mechanism, we want an average power
+(Ptarget) resulting in an amount of time running at full power on a
+specific OPP and idle another amount of time. That could be put in a
+equation::
+
+ P(opp)target = ((Trunning x (P(opp)running) + (Tidle x P(opp)idle)) /
+ (Trunning + Tidle)
+
+ ...
+
+ Tidle = Trunning x ((P(opp)running / P(opp)target) - 1)
+
+At this point if we know the running period for the CPU, that gives us
+the idle injection we need. Alternatively if we have the idle
+injection duration, we can compute the running duration with::
+
+ Trunning = Tidle / ((P(opp)running / P(opp)target) - 1)
+
+Practically, if the running power is less than the targeted power, we
+end up with a negative time value, so obviously the equation usage is
+bound to a power reduction, hence a higher OPP is needed to have the
+running power greater than the targeted power.
+
+However, in this demonstration we ignore three aspects:
+
+ * The static leakage is not defined here, we can introduce it in the
+ equation but assuming it will be zero most of the time as it is
+ difficult to get the values from the SoC vendors
+
+ * The idle state wake up latency (or entry + exit latency) is not
+ taken into account, it must be added in the equation in order to
+ rigorously compute the idle injection
+
+ * The injected idle duration must be greater than the idle state
+ target residency, otherwise we end up consuming more energy and
+ potentially invert the mitigation effect
+
+So the final equation is::
+
+ Trunning = (Tidle - Twakeup ) x
+ (((P(opp)dyn + P(opp)static ) - P(opp)target) / P(opp)target )
diff --git a/Documentation/driver-api/thermal/exynos_thermal.rst b/Documentation/driver-api/thermal/exynos_thermal.rst
new file mode 100644
index 000000000..764df4ab5
--- /dev/null
+++ b/Documentation/driver-api/thermal/exynos_thermal.rst
@@ -0,0 +1,90 @@
+========================
+Kernel driver exynos_tmu
+========================
+
+Supported chips:
+
+* ARM Samsung Exynos4, Exynos5 series of SoC
+
+ Datasheet: Not publicly available
+
+Authors: Donggeun Kim <dg77.kim@samsung.com>
+Authors: Amit Daniel <amit.daniel@samsung.com>
+
+TMU controller Description:
+---------------------------
+
+This driver allows to read temperature inside Samsung Exynos4/5 series of SoC.
+
+The chip only exposes the measured 8-bit temperature code value
+through a register.
+Temperature can be taken from the temperature code.
+There are three equations converting from temperature to temperature code.
+
+The three equations are:
+ 1. Two point trimming::
+
+ Tc = (T - 25) * (TI2 - TI1) / (85 - 25) + TI1
+
+ 2. One point trimming::
+
+ Tc = T + TI1 - 25
+
+ 3. No trimming::
+
+ Tc = T + 50
+
+ Tc:
+ Temperature code, T: Temperature,
+ TI1:
+ Trimming info for 25 degree Celsius (stored at TRIMINFO register)
+ Temperature code measured at 25 degree Celsius which is unchanged
+ TI2:
+ Trimming info for 85 degree Celsius (stored at TRIMINFO register)
+ Temperature code measured at 85 degree Celsius which is unchanged
+
+TMU(Thermal Management Unit) in Exynos4/5 generates interrupt
+when temperature exceeds pre-defined levels.
+The maximum number of configurable threshold is five.
+The threshold levels are defined as follows::
+
+ Level_0: current temperature > trigger_level_0 + threshold
+ Level_1: current temperature > trigger_level_1 + threshold
+ Level_2: current temperature > trigger_level_2 + threshold
+ Level_3: current temperature > trigger_level_3 + threshold
+
+The threshold and each trigger_level are set
+through the corresponding registers.
+
+When an interrupt occurs, this driver notify kernel thermal framework
+with the function exynos_report_trigger.
+Although an interrupt condition for level_0 can be set,
+it can be used to synchronize the cooling action.
+
+TMU driver description:
+-----------------------
+
+The exynos thermal driver is structured as::
+
+ Kernel Core thermal framework
+ (thermal_core.c, step_wise.c, cpufreq_cooling.c)
+ ^
+ |
+ |
+ TMU configuration data -----> TMU Driver <----> Exynos Core thermal wrapper
+ (exynos_tmu_data.c) (exynos_tmu.c) (exynos_thermal_common.c)
+ (exynos_tmu_data.h) (exynos_tmu.h) (exynos_thermal_common.h)
+
+a) TMU configuration data:
+ This consist of TMU register offsets/bitfields
+ described through structure exynos_tmu_registers. Also several
+ other platform data (struct exynos_tmu_platform_data) members
+ are used to configure the TMU.
+b) TMU driver:
+ This component initialises the TMU controller and sets different
+ thresholds. It invokes core thermal implementation with the call
+ exynos_report_trigger.
+c) Exynos Core thermal wrapper:
+ This provides 3 wrapper function to use the
+ Kernel core thermal framework. They are exynos_unregister_thermal,
+ exynos_register_thermal and exynos_report_trigger.
diff --git a/Documentation/driver-api/thermal/exynos_thermal_emulation.rst b/Documentation/driver-api/thermal/exynos_thermal_emulation.rst
new file mode 100644
index 000000000..c21d10838
--- /dev/null
+++ b/Documentation/driver-api/thermal/exynos_thermal_emulation.rst
@@ -0,0 +1,61 @@
+=====================
+Exynos Emulation Mode
+=====================
+
+Copyright (C) 2012 Samsung Electronics
+
+Written by Jonghwa Lee <jonghwa3.lee@samsung.com>
+
+Description
+-----------
+
+Exynos 4x12 (4212, 4412) and 5 series provide emulation mode for thermal
+management unit. Thermal emulation mode supports software debug for
+TMU's operation. User can set temperature manually with software code
+and TMU will read current temperature from user value not from sensor's
+value.
+
+Enabling CONFIG_THERMAL_EMULATION option will make this support
+available. When it's enabled, sysfs node will be created as
+/sys/devices/virtual/thermal/thermal_zone'zone id'/emul_temp.
+
+The sysfs node, 'emul_node', will contain value 0 for the initial state.
+When you input any temperature you want to update to sysfs node, it
+automatically enable emulation mode and current temperature will be
+changed into it.
+
+(Exynos also supports user changeable delay time which would be used to
+delay of changing temperature. However, this node only uses same delay
+of real sensing time, 938us.)
+
+Exynos emulation mode requires synchronous of value changing and
+enabling. It means when you want to update the any value of delay or
+next temperature, then you have to enable emulation mode at the same
+time. (Or you have to keep the mode enabling.) If you don't, it fails to
+change the value to updated one and just use last succeessful value
+repeatedly. That's why this node gives users the right to change
+termerpature only. Just one interface makes it more simply to use.
+
+Disabling emulation mode only requires writing value 0 to sysfs node.
+
+::
+
+
+ TEMP 120 |
+ |
+ 100 |
+ |
+ 80 |
+ | +-----------
+ 60 | | |
+ | +-------------| |
+ 40 | | | |
+ | | | |
+ 20 | | | +----------
+ | | | | |
+ 0 |______________|_____________|__________|__________|_________
+ A A A A TIME
+ |<----->| |<----->| |<----->| |
+ | 938us | | | | | |
+ emulation : 0 50 | 70 | 20 | 0
+ current temp: sensor 50 70 20 sensor
diff --git a/Documentation/driver-api/thermal/index.rst b/Documentation/driver-api/thermal/index.rst
new file mode 100644
index 000000000..030306ffa
--- /dev/null
+++ b/Documentation/driver-api/thermal/index.rst
@@ -0,0 +1,20 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=======
+Thermal
+=======
+
+.. toctree::
+ :maxdepth: 1
+
+ cpu-cooling-api
+ cpu-idle-cooling
+ sysfs-api
+ power_allocator
+
+ exynos_thermal
+ exynos_thermal_emulation
+ intel_powerclamp
+ nouveau_thermal
+ x86_pkg_temperature_thermal
+ intel_dptf
diff --git a/Documentation/driver-api/thermal/intel_dptf.rst b/Documentation/driver-api/thermal/intel_dptf.rst
new file mode 100644
index 000000000..372bdb4d0
--- /dev/null
+++ b/Documentation/driver-api/thermal/intel_dptf.rst
@@ -0,0 +1,272 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============================================================
+Intel(R) Dynamic Platform and Thermal Framework Sysfs Interface
+===============================================================
+
+:Copyright: © 2022 Intel Corporation
+
+:Author: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
+
+Introduction
+------------
+
+Intel(R) Dynamic Platform and Thermal Framework (DPTF) is a platform
+level hardware/software solution for power and thermal management.
+
+As a container for multiple power/thermal technologies, DPTF provides
+a coordinated approach for different policies to effect the hardware
+state of a system.
+
+Since it is a platform level framework, this has several components.
+Some parts of the technology is implemented in the firmware and uses
+ACPI and PCI devices to expose various features for monitoring and
+control. Linux has a set of kernel drivers exposing hardware interface
+to user space. This allows user space thermal solutions like
+"Linux Thermal Daemon" to read platform specific thermal and power
+tables to deliver adequate performance while keeping the system under
+thermal limits.
+
+DPTF ACPI Drivers interface
+----------------------------
+
+:file:`/sys/bus/platform/devices/<N>/uuids`, where <N>
+=INT3400|INTC1040|INTC1041|INTC10A0
+
+``available_uuids`` (RO)
+ A set of UUIDs strings presenting available policies
+ which should be notified to the firmware when the
+ user space can support those policies.
+
+ UUID strings:
+
+ "42A441D6-AE6A-462b-A84B-4A8CE79027D3" : Passive 1
+
+ "3A95C389-E4B8-4629-A526-C52C88626BAE" : Active
+
+ "97C68AE7-15FA-499c-B8C9-5DA81D606E0A" : Critical
+
+ "63BE270F-1C11-48FD-A6F7-3AF253FF3E2D" : Adaptive performance
+
+ "5349962F-71E6-431D-9AE8-0A635B710AEE" : Emergency call
+
+ "9E04115A-AE87-4D1C-9500-0F3E340BFE75" : Passive 2
+
+ "F5A35014-C209-46A4-993A-EB56DE7530A1" : Power Boss
+
+ "6ED722A7-9240-48A5-B479-31EEF723D7CF" : Virtual Sensor
+
+ "16CAF1B7-DD38-40ED-B1C1-1B8A1913D531" : Cooling mode
+
+ "BE84BABF-C4D4-403D-B495-3128FD44dAC1" : HDC
+
+``current_uuid`` (RW)
+ User space can write strings from available UUIDs, one at a
+ time.
+
+:file:`/sys/bus/platform/devices/<N>/`, where <N>
+=INT3400|INTC1040|INTC1041|INTC10A0
+
+``imok`` (WO)
+ User space daemon write 1 to respond to firmware event
+ for sending keep alive notification. User space receives
+ THERMAL_EVENT_KEEP_ALIVE kobject uevent notification when
+ firmware calls for user space to respond with imok ACPI
+ method.
+
+``odvp*`` (RO)
+ Firmware thermal status variable values. Thermal tables
+ calls for different processing based on these variable
+ values.
+
+``data_vault`` (RO)
+ Binary thermal table. Refer to
+ https:/github.com/intel/thermal_daemon for decoding
+ thermal table.
+
+
+ACPI Thermal Relationship table interface
+------------------------------------------
+
+:file:`/dev/acpi_thermal_rel`
+
+ This device provides IOCTL interface to read standard ACPI
+ thermal relationship tables via ACPI methods _TRT and _ART.
+ These IOCTLs are defined in
+ drivers/thermal/intel/int340x_thermal/acpi_thermal_rel.h
+
+ IOCTLs:
+
+ ACPI_THERMAL_GET_TRT_LEN: Get length of TRT table
+
+ ACPI_THERMAL_GET_ART_LEN: Get length of ART table
+
+ ACPI_THERMAL_GET_TRT_COUNT: Number of records in TRT table
+
+ ACPI_THERMAL_GET_ART_COUNT: Number of records in ART table
+
+ ACPI_THERMAL_GET_TRT: Read binary TRT table, length to read is
+ provided via argument to ioctl().
+
+ ACPI_THERMAL_GET_ART: Read binary ART table, length to read is
+ provided via argument to ioctl().
+
+DPTF ACPI Sensor drivers
+-------------------------
+
+DPTF Sensor drivers are presented as standard thermal sysfs thermal_zone.
+
+
+DPTF ACPI Cooling drivers
+--------------------------
+
+DPTF cooling drivers are presented as standard thermal sysfs cooling_device.
+
+
+DPTF Processor thermal PCI Driver interface
+--------------------------------------------
+
+:file:`/sys/bus/pci/devices/0000\:00\:04.0/power_limits/`
+
+Refer to Documentation/power/powercap/powercap.rst for powercap
+ABI.
+
+``power_limit_0_max_uw`` (RO)
+ Maximum powercap sysfs constraint_0_power_limit_uw for Intel RAPL
+
+``power_limit_0_step_uw`` (RO)
+ Power limit increment/decrements for Intel RAPL constraint 0 power limit
+
+``power_limit_0_min_uw`` (RO)
+ Minimum powercap sysfs constraint_0_power_limit_uw for Intel RAPL
+
+``power_limit_0_tmin_us`` (RO)
+ Minimum powercap sysfs constraint_0_time_window_us for Intel RAPL
+
+``power_limit_0_tmax_us`` (RO)
+ Maximum powercap sysfs constraint_0_time_window_us for Intel RAPL
+
+``power_limit_1_max_uw`` (RO)
+ Maximum powercap sysfs constraint_1_power_limit_uw for Intel RAPL
+
+``power_limit_1_step_uw`` (RO)
+ Power limit increment/decrements for Intel RAPL constraint 1 power limit
+
+``power_limit_1_min_uw`` (RO)
+ Minimum powercap sysfs constraint_1_power_limit_uw for Intel RAPL
+
+``power_limit_1_tmin_us`` (RO)
+ Minimum powercap sysfs constraint_1_time_window_us for Intel RAPL
+
+``power_limit_1_tmax_us`` (RO)
+ Maximum powercap sysfs constraint_1_time_window_us for Intel RAPL
+
+:file:`/sys/bus/pci/devices/0000\:00\:04.0/`
+
+``tcc_offset_degree_celsius`` (RW)
+ TCC offset from the critical temperature where hardware will throttle
+ CPU.
+
+:file:`/sys/bus/pci/devices/0000\:00\:04.0/workload_request`
+
+``workload_available_types`` (RO)
+ Available workload types. User space can specify one of the workload type
+ it is currently executing via workload_type. For example: idle, bursty,
+ sustained etc.
+
+``workload_type`` (RW)
+ User space can specify any one of the available workload type using
+ this interface.
+
+DPTF Processor thermal RFIM interface
+--------------------------------------------
+
+RFIM interface allows adjustment of FIVR (Fully Integrated Voltage Regulator)
+and DDR (Double Data Rate)frequencies to avoid RF interference with WiFi and 5G.
+
+Switching voltage regulators (VR) generate radiated EMI or RFI at the
+fundamental frequency and its harmonics. Some harmonics may interfere
+with very sensitive wireless receivers such as Wi-Fi and cellular that
+are integrated into host systems like notebook PCs. One of mitigation
+methods is requesting SOC integrated VR (IVR) switching frequency to a
+small % and shift away the switching noise harmonic interference from
+radio channels. OEM or ODMs can use the driver to control SOC IVR
+operation within the range where it does not impact IVR performance.
+
+DRAM devices of DDR IO interface and their power plane can generate EMI
+at the data rates. Similar to IVR control mechanism, Intel offers a
+mechanism by which DDR data rates can be changed if several conditions
+are met: there is strong RFI interference because of DDR; CPU power
+management has no other restriction in changing DDR data rates;
+PC ODMs enable this feature (real time DDR RFI Mitigation referred to as
+DDR-RFIM) for Wi-Fi from BIOS.
+
+
+FIVR attributes
+
+:file:`/sys/bus/pci/devices/0000\:00\:04.0/fivr/`
+
+``vco_ref_code_lo`` (RW)
+ The VCO reference code is an 11-bit field and controls the FIVR
+ switching frequency. This is the 3-bit LSB field.
+
+``vco_ref_code_hi`` (RW)
+ The VCO reference code is an 11-bit field and controls the FIVR
+ switching frequency. This is the 8-bit MSB field.
+
+``spread_spectrum_pct`` (RW)
+ Set the FIVR spread spectrum clocking percentage
+
+``spread_spectrum_clk_enable`` (RW)
+ Enable/disable of the FIVR spread spectrum clocking feature
+
+``rfi_vco_ref_code`` (RW)
+ This field is a read only status register which reflects the
+ current FIVR switching frequency
+
+``fivr_fffc_rev`` (RW)
+ This field indicated the revision of the FIVR HW.
+
+
+DVFS attributes
+
+:file:`/sys/bus/pci/devices/0000\:00\:04.0/dvfs/`
+
+``rfi_restriction_run_busy`` (RW)
+ Request the restriction of specific DDR data rate and set this
+ value 1. Self reset to 0 after operation.
+
+``rfi_restriction_err_code`` (RW)
+ 0 :Request is accepted, 1:Feature disabled,
+ 2: the request restricts more points than it is allowed
+
+``rfi_restriction_data_rate_Delta`` (RW)
+ Restricted DDR data rate for RFI protection: Lower Limit
+
+``rfi_restriction_data_rate_Base`` (RW)
+ Restricted DDR data rate for RFI protection: Upper Limit
+
+``ddr_data_rate_point_0`` (RO)
+ DDR data rate selection 1st point
+
+``ddr_data_rate_point_1`` (RO)
+ DDR data rate selection 2nd point
+
+``ddr_data_rate_point_2`` (RO)
+ DDR data rate selection 3rd point
+
+``ddr_data_rate_point_3`` (RO)
+ DDR data rate selection 4th point
+
+``rfi_disable (RW)``
+ Disable DDR rate change feature
+
+DPTF Power supply and Battery Interface
+----------------------------------------
+
+Refer to Documentation/ABI/testing/sysfs-platform-dptf
+
+DPTF Fan Control
+----------------------------------------
+
+Refer to Documentation/admin-guide/acpi/fan_performance_states.rst
diff --git a/Documentation/driver-api/thermal/intel_powerclamp.rst b/Documentation/driver-api/thermal/intel_powerclamp.rst
new file mode 100644
index 000000000..3f6dfb0b3
--- /dev/null
+++ b/Documentation/driver-api/thermal/intel_powerclamp.rst
@@ -0,0 +1,320 @@
+=======================
+Intel Powerclamp Driver
+=======================
+
+By:
+ - Arjan van de Ven <arjan@linux.intel.com>
+ - Jacob Pan <jacob.jun.pan@linux.intel.com>
+
+.. Contents:
+
+ (*) Introduction
+ - Goals and Objectives
+
+ (*) Theory of Operation
+ - Idle Injection
+ - Calibration
+
+ (*) Performance Analysis
+ - Effectiveness and Limitations
+ - Power vs Performance
+ - Scalability
+ - Calibration
+ - Comparison with Alternative Techniques
+
+ (*) Usage and Interfaces
+ - Generic Thermal Layer (sysfs)
+ - Kernel APIs (TBD)
+
+INTRODUCTION
+============
+
+Consider the situation where a system’s power consumption must be
+reduced at runtime, due to power budget, thermal constraint, or noise
+level, and where active cooling is not preferred. Software managed
+passive power reduction must be performed to prevent the hardware
+actions that are designed for catastrophic scenarios.
+
+Currently, P-states, T-states (clock modulation), and CPU offlining
+are used for CPU throttling.
+
+On Intel CPUs, C-states provide effective power reduction, but so far
+they’re only used opportunistically, based on workload. With the
+development of intel_powerclamp driver, the method of synchronizing
+idle injection across all online CPU threads was introduced. The goal
+is to achieve forced and controllable C-state residency.
+
+Test/Analysis has been made in the areas of power, performance,
+scalability, and user experience. In many cases, clear advantage is
+shown over taking the CPU offline or modulating the CPU clock.
+
+
+THEORY OF OPERATION
+===================
+
+Idle Injection
+--------------
+
+On modern Intel processors (Nehalem or later), package level C-state
+residency is available in MSRs, thus also available to the kernel.
+
+These MSRs are::
+
+ #define MSR_PKG_C2_RESIDENCY 0x60D
+ #define MSR_PKG_C3_RESIDENCY 0x3F8
+ #define MSR_PKG_C6_RESIDENCY 0x3F9
+ #define MSR_PKG_C7_RESIDENCY 0x3FA
+
+If the kernel can also inject idle time to the system, then a
+closed-loop control system can be established that manages package
+level C-state. The intel_powerclamp driver is conceived as such a
+control system, where the target set point is a user-selected idle
+ratio (based on power reduction), and the error is the difference
+between the actual package level C-state residency ratio and the target idle
+ratio.
+
+Injection is controlled by high priority kernel threads, spawned for
+each online CPU.
+
+These kernel threads, with SCHED_FIFO class, are created to perform
+clamping actions of controlled duty ratio and duration. Each per-CPU
+thread synchronizes its idle time and duration, based on the rounding
+of jiffies, so accumulated errors can be prevented to avoid a jittery
+effect. Threads are also bound to the CPU such that they cannot be
+migrated, unless the CPU is taken offline. In this case, threads
+belong to the offlined CPUs will be terminated immediately.
+
+Running as SCHED_FIFO and relatively high priority, also allows such
+scheme to work for both preemptable and non-preemptable kernels.
+Alignment of idle time around jiffies ensures scalability for HZ
+values. This effect can be better visualized using a Perf timechart.
+The following diagram shows the behavior of kernel thread
+kidle_inject/cpu. During idle injection, it runs monitor/mwait idle
+for a given "duration", then relinquishes the CPU to other tasks,
+until the next time interval.
+
+The NOHZ schedule tick is disabled during idle time, but interrupts
+are not masked. Tests show that the extra wakeups from scheduler tick
+have a dramatic impact on the effectiveness of the powerclamp driver
+on large scale systems (Westmere system with 80 processors).
+
+::
+
+ CPU0
+ ____________ ____________
+ kidle_inject/0 | sleep | mwait | sleep |
+ _________| |________| |_______
+ duration
+ CPU1
+ ____________ ____________
+ kidle_inject/1 | sleep | mwait | sleep |
+ _________| |________| |_______
+ ^
+ |
+ |
+ roundup(jiffies, interval)
+
+Only one CPU is allowed to collect statistics and update global
+control parameters. This CPU is referred to as the controlling CPU in
+this document. The controlling CPU is elected at runtime, with a
+policy that favors BSP, taking into account the possibility of a CPU
+hot-plug.
+
+In terms of dynamics of the idle control system, package level idle
+time is considered largely as a non-causal system where its behavior
+cannot be based on the past or current input. Therefore, the
+intel_powerclamp driver attempts to enforce the desired idle time
+instantly as given input (target idle ratio). After injection,
+powerclamp monitors the actual idle for a given time window and adjust
+the next injection accordingly to avoid over/under correction.
+
+When used in a causal control system, such as a temperature control,
+it is up to the user of this driver to implement algorithms where
+past samples and outputs are included in the feedback. For example, a
+PID-based thermal controller can use the powerclamp driver to
+maintain a desired target temperature, based on integral and
+derivative gains of the past samples.
+
+
+
+Calibration
+-----------
+During scalability testing, it is observed that synchronized actions
+among CPUs become challenging as the number of cores grows. This is
+also true for the ability of a system to enter package level C-states.
+
+To make sure the intel_powerclamp driver scales well, online
+calibration is implemented. The goals for doing such a calibration
+are:
+
+a) determine the effective range of idle injection ratio
+b) determine the amount of compensation needed at each target ratio
+
+Compensation to each target ratio consists of two parts:
+
+ a) steady state error compensation
+ This is to offset the error occurring when the system can
+ enter idle without extra wakeups (such as external interrupts).
+
+ b) dynamic error compensation
+ When an excessive amount of wakeups occurs during idle, an
+ additional idle ratio can be added to quiet interrupts, by
+ slowing down CPU activities.
+
+A debugfs file is provided for the user to examine compensation
+progress and results, such as on a Westmere system::
+
+ [jacob@nex01 ~]$ cat
+ /sys/kernel/debug/intel_powerclamp/powerclamp_calib
+ controlling cpu: 0
+ pct confidence steady dynamic (compensation)
+ 0 0 0 0
+ 1 1 0 0
+ 2 1 1 0
+ 3 3 1 0
+ 4 3 1 0
+ 5 3 1 0
+ 6 3 1 0
+ 7 3 1 0
+ 8 3 1 0
+ ...
+ 30 3 2 0
+ 31 3 2 0
+ 32 3 1 0
+ 33 3 2 0
+ 34 3 1 0
+ 35 3 2 0
+ 36 3 1 0
+ 37 3 2 0
+ 38 3 1 0
+ 39 3 2 0
+ 40 3 3 0
+ 41 3 1 0
+ 42 3 2 0
+ 43 3 1 0
+ 44 3 1 0
+ 45 3 2 0
+ 46 3 3 0
+ 47 3 0 0
+ 48 3 2 0
+ 49 3 3 0
+
+Calibration occurs during runtime. No offline method is available.
+Steady state compensation is used only when confidence levels of all
+adjacent ratios have reached satisfactory level. A confidence level
+is accumulated based on clean data collected at runtime. Data
+collected during a period without extra interrupts is considered
+clean.
+
+To compensate for excessive amounts of wakeup during idle, additional
+idle time is injected when such a condition is detected. Currently,
+we have a simple algorithm to double the injection ratio. A possible
+enhancement might be to throttle the offending IRQ, such as delaying
+EOI for level triggered interrupts. But it is a challenge to be
+non-intrusive to the scheduler or the IRQ core code.
+
+
+CPU Online/Offline
+------------------
+Per-CPU kernel threads are started/stopped upon receiving
+notifications of CPU hotplug activities. The intel_powerclamp driver
+keeps track of clamping kernel threads, even after they are migrated
+to other CPUs, after a CPU offline event.
+
+
+Performance Analysis
+====================
+This section describes the general performance data collected on
+multiple systems, including Westmere (80P) and Ivy Bridge (4P, 8P).
+
+Effectiveness and Limitations
+-----------------------------
+The maximum range that idle injection is allowed is capped at 50
+percent. As mentioned earlier, since interrupts are allowed during
+forced idle time, excessive interrupts could result in less
+effectiveness. The extreme case would be doing a ping -f to generated
+flooded network interrupts without much CPU acknowledgement. In this
+case, little can be done from the idle injection threads. In most
+normal cases, such as scp a large file, applications can be throttled
+by the powerclamp driver, since slowing down the CPU also slows down
+network protocol processing, which in turn reduces interrupts.
+
+When control parameters change at runtime by the controlling CPU, it
+may take an additional period for the rest of the CPUs to catch up
+with the changes. During this time, idle injection is out of sync,
+thus not able to enter package C- states at the expected ratio. But
+this effect is minor, in that in most cases change to the target
+ratio is updated much less frequently than the idle injection
+frequency.
+
+Scalability
+-----------
+Tests also show a minor, but measurable, difference between the 4P/8P
+Ivy Bridge system and the 80P Westmere server under 50% idle ratio.
+More compensation is needed on Westmere for the same amount of
+target idle ratio. The compensation also increases as the idle ratio
+gets larger. The above reason constitutes the need for the
+calibration code.
+
+On the IVB 8P system, compared to an offline CPU, powerclamp can
+achieve up to 40% better performance per watt. (measured by a spin
+counter summed over per CPU counting threads spawned for all running
+CPUs).
+
+Usage and Interfaces
+====================
+The powerclamp driver is registered to the generic thermal layer as a
+cooling device. Currently, it’s not bound to any thermal zones::
+
+ jacob@chromoly:/sys/class/thermal/cooling_device14$ grep . *
+ cur_state:0
+ max_state:50
+ type:intel_powerclamp
+
+cur_state allows user to set the desired idle percentage. Writing 0 to
+cur_state will stop idle injection. Writing a value between 1 and
+max_state will start the idle injection. Reading cur_state returns the
+actual and current idle percentage. This may not be the same value
+set by the user in that current idle percentage depends on workload
+and includes natural idle. When idle injection is disabled, reading
+cur_state returns value -1 instead of 0 which is to avoid confusing
+100% busy state with the disabled state.
+
+Example usage:
+- To inject 25% idle time::
+
+ $ sudo sh -c "echo 25 > /sys/class/thermal/cooling_device80/cur_state
+
+If the system is not busy and has more than 25% idle time already,
+then the powerclamp driver will not start idle injection. Using Top
+will not show idle injection kernel threads.
+
+If the system is busy (spin test below) and has less than 25% natural
+idle time, powerclamp kernel threads will do idle injection. Forced
+idle time is accounted as normal idle in that common code path is
+taken as the idle task.
+
+In this example, 24.1% idle is shown. This helps the system admin or
+user determine the cause of slowdown, when a powerclamp driver is in action::
+
+
+ Tasks: 197 total, 1 running, 196 sleeping, 0 stopped, 0 zombie
+ Cpu(s): 71.2%us, 4.7%sy, 0.0%ni, 24.1%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
+ Mem: 3943228k total, 1689632k used, 2253596k free, 74960k buffers
+ Swap: 4087804k total, 0k used, 4087804k free, 945336k cached
+
+ PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
+ 3352 jacob 20 0 262m 644 428 S 286 0.0 0:17.16 spin
+ 3341 root -51 0 0 0 0 D 25 0.0 0:01.62 kidle_inject/0
+ 3344 root -51 0 0 0 0 D 25 0.0 0:01.60 kidle_inject/3
+ 3342 root -51 0 0 0 0 D 25 0.0 0:01.61 kidle_inject/1
+ 3343 root -51 0 0 0 0 D 25 0.0 0:01.60 kidle_inject/2
+ 2935 jacob 20 0 696m 125m 35m S 5 3.3 0:31.11 firefox
+ 1546 root 20 0 158m 20m 6640 S 3 0.5 0:26.97 Xorg
+ 2100 jacob 20 0 1223m 88m 30m S 3 2.3 0:23.68 compiz
+
+Tests have shown that by using the powerclamp driver as a cooling
+device, a PID based userspace thermal controller can manage to
+control CPU temperature effectively, when no other thermal influence
+is added. For example, a UltraBook user can compile the kernel under
+certain temperature (below most active trip points).
diff --git a/Documentation/driver-api/thermal/nouveau_thermal.rst b/Documentation/driver-api/thermal/nouveau_thermal.rst
new file mode 100644
index 000000000..aa10db6df
--- /dev/null
+++ b/Documentation/driver-api/thermal/nouveau_thermal.rst
@@ -0,0 +1,96 @@
+=====================
+Kernel driver nouveau
+=====================
+
+Supported chips:
+
+* NV43+
+
+Authors: Martin Peres (mupuf) <martin.peres@free.fr>
+
+Description
+-----------
+
+This driver allows to read the GPU core temperature, drive the GPU fan and
+set temperature alarms.
+
+Currently, due to the absence of in-kernel API to access HWMON drivers, Nouveau
+cannot access any of the i2c external monitoring chips it may find. If you
+have one of those, temperature and/or fan management through Nouveau's HWMON
+interface is likely not to work. This document may then not cover your situation
+entirely.
+
+Temperature management
+----------------------
+
+Temperature is exposed under as a read-only HWMON attribute temp1_input.
+
+In order to protect the GPU from overheating, Nouveau supports 4 configurable
+temperature thresholds:
+
+ * Fan_boost:
+ Fan speed is set to 100% when reaching this temperature;
+ * Downclock:
+ The GPU will be downclocked to reduce its power dissipation;
+ * Critical:
+ The GPU is put on hold to further lower power dissipation;
+ * Shutdown:
+ Shut the computer down to protect your GPU.
+
+WARNING:
+ Some of these thresholds may not be used by Nouveau depending
+ on your chipset.
+
+The default value for these thresholds comes from the GPU's vbios. These
+thresholds can be configured thanks to the following HWMON attributes:
+
+ * Fan_boost: temp1_auto_point1_temp and temp1_auto_point1_temp_hyst;
+ * Downclock: temp1_max and temp1_max_hyst;
+ * Critical: temp1_crit and temp1_crit_hyst;
+ * Shutdown: temp1_emergency and temp1_emergency_hyst.
+
+NOTE: Remember that the values are stored as milli degrees Celsius. Don't forget
+to multiply!
+
+Fan management
+--------------
+
+Not all cards have a drivable fan. If you do, then the following HWMON
+attributes should be available:
+
+ * pwm1_enable:
+ Current fan management mode (NONE, MANUAL or AUTO);
+ * pwm1:
+ Current PWM value (power percentage);
+ * pwm1_min:
+ The minimum PWM speed allowed;
+ * pwm1_max:
+ The maximum PWM speed allowed (bypassed when hitting Fan_boost);
+
+You may also have the following attribute:
+
+ * fan1_input:
+ Speed in RPM of your fan.
+
+Your fan can be driven in different modes:
+
+ * 0: The fan is left untouched;
+ * 1: The fan can be driven in manual (use pwm1 to change the speed);
+ * 2; The fan is driven automatically depending on the temperature.
+
+NOTE:
+ Be sure to use the manual mode if you want to drive the fan speed manually
+
+NOTE2:
+ When operating in manual mode outside the vbios-defined
+ [PWM_min, PWM_max] range, the reported fan speed (RPM) may not be accurate
+ depending on your hardware.
+
+Bug reports
+-----------
+
+Thermal management on Nouveau is new and may not work on all cards. If you have
+inquiries, please ping mupuf on IRC (#nouveau, OFTC).
+
+Bug reports should be filled on Freedesktop's bug tracker. Please follow
+https://nouveau.freedesktop.org/wiki/Bugs
diff --git a/Documentation/driver-api/thermal/power_allocator.rst b/Documentation/driver-api/thermal/power_allocator.rst
new file mode 100644
index 000000000..aa5f66552
--- /dev/null
+++ b/Documentation/driver-api/thermal/power_allocator.rst
@@ -0,0 +1,281 @@
+=================================
+Power allocator governor tunables
+=================================
+
+Trip points
+-----------
+
+The governor works optimally with the following two passive trip points:
+
+1. "switch on" trip point: temperature above which the governor
+ control loop starts operating. This is the first passive trip
+ point of the thermal zone.
+
+2. "desired temperature" trip point: it should be higher than the
+ "switch on" trip point. This the target temperature the governor
+ is controlling for. This is the last passive trip point of the
+ thermal zone.
+
+PID Controller
+--------------
+
+The power allocator governor implements a
+Proportional-Integral-Derivative controller (PID controller) with
+temperature as the control input and power as the controlled output:
+
+ P_max = k_p * e + k_i * err_integral + k_d * diff_err + sustainable_power
+
+where
+ - e = desired_temperature - current_temperature
+ - err_integral is the sum of previous errors
+ - diff_err = e - previous_error
+
+It is similar to the one depicted below::
+
+ k_d
+ |
+ current_temp |
+ | v
+ | +----------+ +---+
+ | +----->| diff_err |-->| X |------+
+ | | +----------+ +---+ |
+ | | | tdp actor
+ | | k_i | | get_requested_power()
+ | | | | | | |
+ | | | | | | | ...
+ v | v v v v v
+ +---+ | +-------+ +---+ +---+ +---+ +----------+
+ | S |-----+----->| sum e |----->| X |--->| S |-->| S |-->|power |
+ +---+ | +-------+ +---+ +---+ +---+ |allocation|
+ ^ | ^ +----------+
+ | | | | |
+ | | +---+ | | |
+ | +------->| X |-------------------+ v v
+ | +---+ granted performance
+ desired_temperature ^
+ |
+ |
+ k_po/k_pu
+
+Sustainable power
+-----------------
+
+An estimate of the sustainable dissipatable power (in mW) should be
+provided while registering the thermal zone. This estimates the
+sustained power that can be dissipated at the desired control
+temperature. This is the maximum sustained power for allocation at
+the desired maximum temperature. The actual sustained power can vary
+for a number of reasons. The closed loop controller will take care of
+variations such as environmental conditions, and some factors related
+to the speed-grade of the silicon. `sustainable_power` is therefore
+simply an estimate, and may be tuned to affect the aggressiveness of
+the thermal ramp. For reference, the sustainable power of a 4" phone
+is typically 2000mW, while on a 10" tablet is around 4500mW (may vary
+depending on screen size). It is possible to have the power value
+expressed in an abstract scale. The sustained power should be aligned
+to the scale used by the related cooling devices.
+
+If you are using device tree, do add it as a property of the
+thermal-zone. For example::
+
+ thermal-zones {
+ soc_thermal {
+ polling-delay = <1000>;
+ polling-delay-passive = <100>;
+ sustainable-power = <2500>;
+ ...
+
+Instead, if the thermal zone is registered from the platform code, pass a
+`thermal_zone_params` that has a `sustainable_power`. If no
+`thermal_zone_params` were being passed, then something like below
+will suffice::
+
+ static const struct thermal_zone_params tz_params = {
+ .sustainable_power = 3500,
+ };
+
+and then pass `tz_params` as the 5th parameter to
+`thermal_zone_device_register()`
+
+k_po and k_pu
+-------------
+
+The implementation of the PID controller in the power allocator
+thermal governor allows the configuration of two proportional term
+constants: `k_po` and `k_pu`. `k_po` is the proportional term
+constant during temperature overshoot periods (current temperature is
+above "desired temperature" trip point). Conversely, `k_pu` is the
+proportional term constant during temperature undershoot periods
+(current temperature below "desired temperature" trip point).
+
+These controls are intended as the primary mechanism for configuring
+the permitted thermal "ramp" of the system. For instance, a lower
+`k_pu` value will provide a slower ramp, at the cost of capping
+available capacity at a low temperature. On the other hand, a high
+value of `k_pu` will result in the governor granting very high power
+while temperature is low, and may lead to temperature overshooting.
+
+The default value for `k_pu` is::
+
+ 2 * sustainable_power / (desired_temperature - switch_on_temp)
+
+This means that at `switch_on_temp` the output of the controller's
+proportional term will be 2 * `sustainable_power`. The default value
+for `k_po` is::
+
+ sustainable_power / (desired_temperature - switch_on_temp)
+
+Focusing on the proportional and feed forward values of the PID
+controller equation we have::
+
+ P_max = k_p * e + sustainable_power
+
+The proportional term is proportional to the difference between the
+desired temperature and the current one. When the current temperature
+is the desired one, then the proportional component is zero and
+`P_max` = `sustainable_power`. That is, the system should operate in
+thermal equilibrium under constant load. `sustainable_power` is only
+an estimate, which is the reason for closed-loop control such as this.
+
+Expanding `k_pu` we get::
+
+ P_max = 2 * sustainable_power * (T_set - T) / (T_set - T_on) +
+ sustainable_power
+
+where:
+
+ - T_set is the desired temperature
+ - T is the current temperature
+ - T_on is the switch on temperature
+
+When the current temperature is the switch_on temperature, the above
+formula becomes::
+
+ P_max = 2 * sustainable_power * (T_set - T_on) / (T_set - T_on) +
+ sustainable_power = 2 * sustainable_power + sustainable_power =
+ 3 * sustainable_power
+
+Therefore, the proportional term alone linearly decreases power from
+3 * `sustainable_power` to `sustainable_power` as the temperature
+rises from the switch on temperature to the desired temperature.
+
+k_i and integral_cutoff
+-----------------------
+
+`k_i` configures the PID loop's integral term constant. This term
+allows the PID controller to compensate for long term drift and for
+the quantized nature of the output control: cooling devices can't set
+the exact power that the governor requests. When the temperature
+error is below `integral_cutoff`, errors are accumulated in the
+integral term. This term is then multiplied by `k_i` and the result
+added to the output of the controller. Typically `k_i` is set low (1
+or 2) and `integral_cutoff` is 0.
+
+k_d
+---
+
+`k_d` configures the PID loop's derivative term constant. It's
+recommended to leave it as the default: 0.
+
+Cooling device power API
+========================
+
+Cooling devices controlled by this governor must supply the additional
+"power" API in their `cooling_device_ops`. It consists on three ops:
+
+1. ::
+
+ int get_requested_power(struct thermal_cooling_device *cdev,
+ struct thermal_zone_device *tz, u32 *power);
+
+
+@cdev:
+ The `struct thermal_cooling_device` pointer
+@tz:
+ thermal zone in which we are currently operating
+@power:
+ pointer in which to store the calculated power
+
+`get_requested_power()` calculates the power requested by the device
+in milliwatts and stores it in @power . It should return 0 on
+success, -E* on failure. This is currently used by the power
+allocator governor to calculate how much power to give to each cooling
+device.
+
+2. ::
+
+ int state2power(struct thermal_cooling_device *cdev, struct
+ thermal_zone_device *tz, unsigned long state,
+ u32 *power);
+
+@cdev:
+ The `struct thermal_cooling_device` pointer
+@tz:
+ thermal zone in which we are currently operating
+@state:
+ A cooling device state
+@power:
+ pointer in which to store the equivalent power
+
+Convert cooling device state @state into power consumption in
+milliwatts and store it in @power. It should return 0 on success, -E*
+on failure. This is currently used by thermal core to calculate the
+maximum power that an actor can consume.
+
+3. ::
+
+ int power2state(struct thermal_cooling_device *cdev, u32 power,
+ unsigned long *state);
+
+@cdev:
+ The `struct thermal_cooling_device` pointer
+@power:
+ power in milliwatts
+@state:
+ pointer in which to store the resulting state
+
+Calculate a cooling device state that would make the device consume at
+most @power mW and store it in @state. It should return 0 on success,
+-E* on failure. This is currently used by the thermal core to convert
+a given power set by the power allocator governor to a state that the
+cooling device can set. It is a function because this conversion may
+depend on external factors that may change so this function should the
+best conversion given "current circumstances".
+
+Cooling device weights
+----------------------
+
+Weights are a mechanism to bias the allocation among cooling
+devices. They express the relative power efficiency of different
+cooling devices. Higher weight can be used to express higher power
+efficiency. Weighting is relative such that if each cooling device
+has a weight of one they are considered equal. This is particularly
+useful in heterogeneous systems where two cooling devices may perform
+the same kind of compute, but with different efficiency. For example,
+a system with two different types of processors.
+
+If the thermal zone is registered using
+`thermal_zone_device_register()` (i.e., platform code), then weights
+are passed as part of the thermal zone's `thermal_bind_parameters`.
+If the platform is registered using device tree, then they are passed
+as the `contribution` property of each map in the `cooling-maps` node.
+
+Limitations of the power allocator governor
+===========================================
+
+The power allocator governor's PID controller works best if there is a
+periodic tick. If you have a driver that calls
+`thermal_zone_device_update()` (or anything that ends up calling the
+governor's `throttle()` function) repetitively, the governor response
+won't be very good. Note that this is not particular to this
+governor, step-wise will also misbehave if you call its throttle()
+faster than the normal thermal framework tick (due to interrupts for
+example) as it will overreact.
+
+Energy Model requirements
+=========================
+
+Another important thing is the consistent scale of the power values
+provided by the cooling devices. All of the cooling devices in a single
+thermal zone should have power values reported either in milli-Watts
+or scaled to the same 'abstract scale'.
diff --git a/Documentation/driver-api/thermal/sysfs-api.rst b/Documentation/driver-api/thermal/sysfs-api.rst
new file mode 100644
index 000000000..2e0f79a9e
--- /dev/null
+++ b/Documentation/driver-api/thermal/sysfs-api.rst
@@ -0,0 +1,535 @@
+===================================
+Generic Thermal Sysfs driver How To
+===================================
+
+Written by Sujith Thomas <sujith.thomas@intel.com>, Zhang Rui <rui.zhang@intel.com>
+
+Updated: 2 January 2008
+
+Copyright (c) 2008 Intel Corporation
+
+
+0. Introduction
+===============
+
+The generic thermal sysfs provides a set of interfaces for thermal zone
+devices (sensors) and thermal cooling devices (fan, processor...) to register
+with the thermal management solution and to be a part of it.
+
+This how-to focuses on enabling new thermal zone and cooling devices to
+participate in thermal management.
+This solution is platform independent and any type of thermal zone devices
+and cooling devices should be able to make use of the infrastructure.
+
+The main task of the thermal sysfs driver is to expose thermal zone attributes
+as well as cooling device attributes to the user space.
+An intelligent thermal management application can make decisions based on
+inputs from thermal zone attributes (the current temperature and trip point
+temperature) and throttle appropriate devices.
+
+- `[0-*]` denotes any positive number starting from 0
+- `[1-*]` denotes any positive number starting from 1
+
+1. thermal sysfs driver interface functions
+===========================================
+
+1.1 thermal zone device interface
+---------------------------------
+
+ ::
+
+ struct thermal_zone_device
+ *thermal_zone_device_register(char *type,
+ int trips, int mask, void *devdata,
+ struct thermal_zone_device_ops *ops,
+ const struct thermal_zone_params *tzp,
+ int passive_delay, int polling_delay))
+
+ This interface function adds a new thermal zone device (sensor) to
+ /sys/class/thermal folder as `thermal_zone[0-*]`. It tries to bind all the
+ thermal cooling devices registered at the same time.
+
+ type:
+ the thermal zone type.
+ trips:
+ the total number of trip points this thermal zone supports.
+ mask:
+ Bit string: If 'n'th bit is set, then trip point 'n' is writable.
+ devdata:
+ device private data
+ ops:
+ thermal zone device call-backs.
+
+ .bind:
+ bind the thermal zone device with a thermal cooling device.
+ .unbind:
+ unbind the thermal zone device with a thermal cooling device.
+ .get_temp:
+ get the current temperature of the thermal zone.
+ .set_trips:
+ set the trip points window. Whenever the current temperature
+ is updated, the trip points immediately below and above the
+ current temperature are found.
+ .get_mode:
+ get the current mode (enabled/disabled) of the thermal zone.
+
+ - "enabled" means the kernel thermal management is
+ enabled.
+ - "disabled" will prevent kernel thermal driver action
+ upon trip points so that user applications can take
+ charge of thermal management.
+ .set_mode:
+ set the mode (enabled/disabled) of the thermal zone.
+ .get_trip_type:
+ get the type of certain trip point.
+ .get_trip_temp:
+ get the temperature above which the certain trip point
+ will be fired.
+ .set_emul_temp:
+ set the emulation temperature which helps in debugging
+ different threshold temperature points.
+ tzp:
+ thermal zone platform parameters.
+ passive_delay:
+ number of milliseconds to wait between polls when
+ performing passive cooling.
+ polling_delay:
+ number of milliseconds to wait between polls when checking
+ whether trip points have been crossed (0 for interrupt driven systems).
+
+ ::
+
+ void thermal_zone_device_unregister(struct thermal_zone_device *tz)
+
+ This interface function removes the thermal zone device.
+ It deletes the corresponding entry from /sys/class/thermal folder and
+ unbinds all the thermal cooling devices it uses.
+
+ ::
+
+ struct thermal_zone_device
+ *thermal_zone_of_sensor_register(struct device *dev, int sensor_id,
+ void *data,
+ const struct thermal_zone_of_device_ops *ops)
+
+ This interface adds a new sensor to a DT thermal zone.
+ This function will search the list of thermal zones described in
+ device tree and look for the zone that refer to the sensor device
+ pointed by dev->of_node as temperature providers. For the zone
+ pointing to the sensor node, the sensor will be added to the DT
+ thermal zone device.
+
+ The parameters for this interface are:
+
+ dev:
+ Device node of sensor containing valid node pointer in
+ dev->of_node.
+ sensor_id:
+ a sensor identifier, in case the sensor IP has more
+ than one sensors
+ data:
+ a private pointer (owned by the caller) that will be
+ passed back, when a temperature reading is needed.
+ ops:
+ `struct thermal_zone_of_device_ops *`.
+
+ ============== =======================================
+ get_temp a pointer to a function that reads the
+ sensor temperature. This is mandatory
+ callback provided by sensor driver.
+ set_trips a pointer to a function that sets a
+ temperature window. When this window is
+ left the driver must inform the thermal
+ core via thermal_zone_device_update.
+ get_trend a pointer to a function that reads the
+ sensor temperature trend.
+ set_emul_temp a pointer to a function that sets
+ sensor emulated temperature.
+ ============== =======================================
+
+ The thermal zone temperature is provided by the get_temp() function
+ pointer of thermal_zone_of_device_ops. When called, it will
+ have the private pointer @data back.
+
+ It returns error pointer if fails otherwise valid thermal zone device
+ handle. Caller should check the return handle with IS_ERR() for finding
+ whether success or not.
+
+ ::
+
+ void thermal_zone_of_sensor_unregister(struct device *dev,
+ struct thermal_zone_device *tzd)
+
+ This interface unregisters a sensor from a DT thermal zone which was
+ successfully added by interface thermal_zone_of_sensor_register().
+ This function removes the sensor callbacks and private data from the
+ thermal zone device registered with thermal_zone_of_sensor_register()
+ interface. It will also silent the zone by remove the .get_temp() and
+ get_trend() thermal zone device callbacks.
+
+ ::
+
+ struct thermal_zone_device
+ *devm_thermal_zone_of_sensor_register(struct device *dev,
+ int sensor_id,
+ void *data,
+ const struct thermal_zone_of_device_ops *ops)
+
+ This interface is resource managed version of
+ thermal_zone_of_sensor_register().
+
+ All details of thermal_zone_of_sensor_register() described in
+ section 1.1.3 is applicable here.
+
+ The benefit of using this interface to register sensor is that it
+ is not require to explicitly call thermal_zone_of_sensor_unregister()
+ in error path or during driver unbinding as this is done by driver
+ resource manager.
+
+ ::
+
+ void devm_thermal_zone_of_sensor_unregister(struct device *dev,
+ struct thermal_zone_device *tzd)
+
+ This interface is resource managed version of
+ thermal_zone_of_sensor_unregister().
+ All details of thermal_zone_of_sensor_unregister() described in
+ section 1.1.4 is applicable here.
+ Normally this function will not need to be called and the resource
+ management code will ensure that the resource is freed.
+
+ ::
+
+ int thermal_zone_get_slope(struct thermal_zone_device *tz)
+
+ This interface is used to read the slope attribute value
+ for the thermal zone device, which might be useful for platform
+ drivers for temperature calculations.
+
+ ::
+
+ int thermal_zone_get_offset(struct thermal_zone_device *tz)
+
+ This interface is used to read the offset attribute value
+ for the thermal zone device, which might be useful for platform
+ drivers for temperature calculations.
+
+1.2 thermal cooling device interface
+------------------------------------
+
+
+ ::
+
+ struct thermal_cooling_device
+ *thermal_cooling_device_register(char *name,
+ void *devdata, struct thermal_cooling_device_ops *)
+
+ This interface function adds a new thermal cooling device (fan/processor/...)
+ to /sys/class/thermal/ folder as `cooling_device[0-*]`. It tries to bind itself
+ to all the thermal zone devices registered at the same time.
+
+ name:
+ the cooling device name.
+ devdata:
+ device private data.
+ ops:
+ thermal cooling devices call-backs.
+
+ .get_max_state:
+ get the Maximum throttle state of the cooling device.
+ .get_cur_state:
+ get the Currently requested throttle state of the
+ cooling device.
+ .set_cur_state:
+ set the Current throttle state of the cooling device.
+
+ ::
+
+ void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
+
+ This interface function removes the thermal cooling device.
+ It deletes the corresponding entry from /sys/class/thermal folder and
+ unbinds itself from all the thermal zone devices using it.
+
+1.3 interface for binding a thermal zone device with a thermal cooling device
+-----------------------------------------------------------------------------
+
+ ::
+
+ int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
+ int trip, struct thermal_cooling_device *cdev,
+ unsigned long upper, unsigned long lower, unsigned int weight);
+
+ This interface function binds a thermal cooling device to a particular trip
+ point of a thermal zone device.
+
+ This function is usually called in the thermal zone device .bind callback.
+
+ tz:
+ the thermal zone device
+ cdev:
+ thermal cooling device
+ trip:
+ indicates which trip point in this thermal zone the cooling device
+ is associated with.
+ upper:
+ the Maximum cooling state for this trip point.
+ THERMAL_NO_LIMIT means no upper limit,
+ and the cooling device can be in max_state.
+ lower:
+ the Minimum cooling state can be used for this trip point.
+ THERMAL_NO_LIMIT means no lower limit,
+ and the cooling device can be in cooling state 0.
+ weight:
+ the influence of this cooling device in this thermal
+ zone. See 1.4.1 below for more information.
+
+ ::
+
+ int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
+ int trip, struct thermal_cooling_device *cdev);
+
+ This interface function unbinds a thermal cooling device from a particular
+ trip point of a thermal zone device. This function is usually called in
+ the thermal zone device .unbind callback.
+
+ tz:
+ the thermal zone device
+ cdev:
+ thermal cooling device
+ trip:
+ indicates which trip point in this thermal zone the cooling device
+ is associated with.
+
+1.4 Thermal Zone Parameters
+---------------------------
+
+ ::
+
+ struct thermal_bind_params
+
+ This structure defines the following parameters that are used to bind
+ a zone with a cooling device for a particular trip point.
+
+ .cdev:
+ The cooling device pointer
+ .weight:
+ The 'influence' of a particular cooling device on this
+ zone. This is relative to the rest of the cooling
+ devices. For example, if all cooling devices have a
+ weight of 1, then they all contribute the same. You can
+ use percentages if you want, but it's not mandatory. A
+ weight of 0 means that this cooling device doesn't
+ contribute to the cooling of this zone unless all cooling
+ devices have a weight of 0. If all weights are 0, then
+ they all contribute the same.
+ .trip_mask:
+ This is a bit mask that gives the binding relation between
+ this thermal zone and cdev, for a particular trip point.
+ If nth bit is set, then the cdev and thermal zone are bound
+ for trip point n.
+ .binding_limits:
+ This is an array of cooling state limits. Must have
+ exactly 2 * thermal_zone.number_of_trip_points. It is an
+ array consisting of tuples <lower-state upper-state> of
+ state limits. Each trip will be associated with one state
+ limit tuple when binding. A NULL pointer means
+ <THERMAL_NO_LIMITS THERMAL_NO_LIMITS> on all trips.
+ These limits are used when binding a cdev to a trip point.
+ .match:
+ This call back returns success(0) if the 'tz and cdev' need to
+ be bound, as per platform data.
+
+ ::
+
+ struct thermal_zone_params
+
+ This structure defines the platform level parameters for a thermal zone.
+ This data, for each thermal zone should come from the platform layer.
+ This is an optional feature where some platforms can choose not to
+ provide this data.
+
+ .governor_name:
+ Name of the thermal governor used for this zone
+ .no_hwmon:
+ a boolean to indicate if the thermal to hwmon sysfs interface
+ is required. when no_hwmon == false, a hwmon sysfs interface
+ will be created. when no_hwmon == true, nothing will be done.
+ In case the thermal_zone_params is NULL, the hwmon interface
+ will be created (for backward compatibility).
+ .num_tbps:
+ Number of thermal_bind_params entries for this zone
+ .tbp:
+ thermal_bind_params entries
+
+2. sysfs attributes structure
+=============================
+
+== ================
+RO read only value
+WO write only value
+RW read/write value
+== ================
+
+Thermal sysfs attributes will be represented under /sys/class/thermal.
+Hwmon sysfs I/F extension is also available under /sys/class/hwmon
+if hwmon is compiled in or built as a module.
+
+Thermal zone device sys I/F, created once it's registered::
+
+ /sys/class/thermal/thermal_zone[0-*]:
+ |---type: Type of the thermal zone
+ |---temp: Current temperature
+ |---mode: Working mode of the thermal zone
+ |---policy: Thermal governor used for this zone
+ |---available_policies: Available thermal governors for this zone
+ |---trip_point_[0-*]_temp: Trip point temperature
+ |---trip_point_[0-*]_type: Trip point type
+ |---trip_point_[0-*]_hyst: Hysteresis value for this trip point
+ |---emul_temp: Emulated temperature set node
+ |---sustainable_power: Sustainable dissipatable power
+ |---k_po: Proportional term during temperature overshoot
+ |---k_pu: Proportional term during temperature undershoot
+ |---k_i: PID's integral term in the power allocator gov
+ |---k_d: PID's derivative term in the power allocator
+ |---integral_cutoff: Offset above which errors are accumulated
+ |---slope: Slope constant applied as linear extrapolation
+ |---offset: Offset constant applied as linear extrapolation
+
+Thermal cooling device sys I/F, created once it's registered::
+
+ /sys/class/thermal/cooling_device[0-*]:
+ |---type: Type of the cooling device(processor/fan/...)
+ |---max_state: Maximum cooling state of the cooling device
+ |---cur_state: Current cooling state of the cooling device
+ |---stats: Directory containing cooling device's statistics
+ |---stats/reset: Writing any value resets the statistics
+ |---stats/time_in_state_ms: Time (msec) spent in various cooling states
+ |---stats/total_trans: Total number of times cooling state is changed
+ |---stats/trans_table: Cooling state transition table
+
+
+Then next two dynamic attributes are created/removed in pairs. They represent
+the relationship between a thermal zone and its associated cooling device.
+They are created/removed for each successful execution of
+thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
+
+::
+
+ /sys/class/thermal/thermal_zone[0-*]:
+ |---cdev[0-*]: [0-*]th cooling device in current thermal zone
+ |---cdev[0-*]_trip_point: Trip point that cdev[0-*] is associated with
+ |---cdev[0-*]_weight: Influence of the cooling device in
+ this thermal zone
+
+Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
+the generic thermal driver also creates a hwmon sysfs I/F for each _type_
+of thermal zone device. E.g. the generic thermal driver registers one hwmon
+class device and build the associated hwmon sysfs I/F for all the registered
+ACPI thermal zones.
+
+Please read Documentation/ABI/testing/sysfs-class-thermal for thermal
+zone and cooling device attribute details.
+
+::
+
+ /sys/class/hwmon/hwmon[0-*]:
+ |---name: The type of the thermal zone devices
+ |---temp[1-*]_input: The current temperature of thermal zone [1-*]
+ |---temp[1-*]_critical: The critical trip point of thermal zone [1-*]
+
+Please read Documentation/hwmon/sysfs-interface.rst for additional information.
+
+3. A simple implementation
+==========================
+
+ACPI thermal zone may support multiple trip points like critical, hot,
+passive, active. If an ACPI thermal zone supports critical, passive,
+active[0] and active[1] at the same time, it may register itself as a
+thermal_zone_device (thermal_zone1) with 4 trip points in all.
+It has one processor and one fan, which are both registered as
+thermal_cooling_device. Both are considered to have the same
+effectiveness in cooling the thermal zone.
+
+If the processor is listed in _PSL method, and the fan is listed in _AL0
+method, the sys I/F structure will be built like this::
+
+ /sys/class/thermal:
+ |thermal_zone1:
+ |---type: acpitz
+ |---temp: 37000
+ |---mode: enabled
+ |---policy: step_wise
+ |---available_policies: step_wise fair_share
+ |---trip_point_0_temp: 100000
+ |---trip_point_0_type: critical
+ |---trip_point_1_temp: 80000
+ |---trip_point_1_type: passive
+ |---trip_point_2_temp: 70000
+ |---trip_point_2_type: active0
+ |---trip_point_3_temp: 60000
+ |---trip_point_3_type: active1
+ |---cdev0: --->/sys/class/thermal/cooling_device0
+ |---cdev0_trip_point: 1 /* cdev0 can be used for passive */
+ |---cdev0_weight: 1024
+ |---cdev1: --->/sys/class/thermal/cooling_device3
+ |---cdev1_trip_point: 2 /* cdev1 can be used for active[0]*/
+ |---cdev1_weight: 1024
+
+ |cooling_device0:
+ |---type: Processor
+ |---max_state: 8
+ |---cur_state: 0
+
+ |cooling_device3:
+ |---type: Fan
+ |---max_state: 2
+ |---cur_state: 0
+
+ /sys/class/hwmon:
+ |hwmon0:
+ |---name: acpitz
+ |---temp1_input: 37000
+ |---temp1_crit: 100000
+
+4. Export Symbol APIs
+=====================
+
+4.1. get_tz_trend
+-----------------
+
+This function returns the trend of a thermal zone, i.e the rate of change
+of temperature of the thermal zone. Ideally, the thermal sensor drivers
+are supposed to implement the callback. If they don't, the thermal
+framework calculated the trend by comparing the previous and the current
+temperature values.
+
+4.2. get_thermal_instance
+-------------------------
+
+This function returns the thermal_instance corresponding to a given
+{thermal_zone, cooling_device, trip_point} combination. Returns NULL
+if such an instance does not exist.
+
+4.3. thermal_cdev_update
+------------------------
+
+This function serves as an arbitrator to set the state of a cooling
+device. It sets the cooling device to the deepest cooling state if
+possible.
+
+5. thermal_emergency_poweroff
+=============================
+
+On an event of critical trip temperature crossing the thermal framework
+shuts down the system by calling hw_protection_shutdown(). The
+hw_protection_shutdown() first attempts to perform an orderly shutdown
+but accepts a delay after which it proceeds doing a forced power-off
+or as last resort an emergency_restart.
+
+The delay should be carefully profiled so as to give adequate time for
+orderly poweroff.
+
+If the delay is set to 0 emergency poweroff will not be supported. So a
+carefully profiled non-zero positive value is a must for emergency
+poweroff to be triggered.
diff --git a/Documentation/driver-api/thermal/x86_pkg_temperature_thermal.rst b/Documentation/driver-api/thermal/x86_pkg_temperature_thermal.rst
new file mode 100644
index 000000000..2ac42ccd2
--- /dev/null
+++ b/Documentation/driver-api/thermal/x86_pkg_temperature_thermal.rst
@@ -0,0 +1,55 @@
+===================================
+Kernel driver: x86_pkg_temp_thermal
+===================================
+
+Supported chips:
+
+* x86: with package level thermal management
+
+(Verify using: CPUID.06H:EAX[bit 6] =1)
+
+Authors: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
+
+Reference
+---------
+
+Intel® 64 and IA-32 Architectures Software Developer’s Manual (Jan, 2013):
+Chapter 14.6: PACKAGE LEVEL THERMAL MANAGEMENT
+
+Description
+-----------
+
+This driver register CPU digital temperature package level sensor as a thermal
+zone with maximum two user mode configurable trip points. Number of trip points
+depends on the capability of the package. Once the trip point is violated,
+user mode can receive notification via thermal notification mechanism and can
+take any action to control temperature.
+
+
+Threshold management
+--------------------
+Each package will register as a thermal zone under /sys/class/thermal.
+
+Example::
+
+ /sys/class/thermal/thermal_zone1
+
+This contains two trip points:
+
+- trip_point_0_temp
+- trip_point_1_temp
+
+User can set any temperature between 0 to TJ-Max temperature. Temperature units
+are in milli-degree Celsius. Refer to "Documentation/driver-api/thermal/sysfs-api.rst" for
+thermal sys-fs details.
+
+Any value other than 0 in these trip points, can trigger thermal notifications.
+Setting 0, stops sending thermal notifications.
+
+Thermal notifications:
+To get kobject-uevent notifications, set the thermal zone
+policy to "user_space".
+
+For example::
+
+ echo -n "user_space" > policy