Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+.. SPDX-License-Identifier: GPL-2.0
+
+=======================================================
+Legacy Documentation of CPU Performance Scaling Drivers
+=======================================================
+
+Included below are historic documents describing assorted
+:doc:`CPU performance scaling <cpufreq>` drivers.  They are reproduced verbatim,
+with the original white space formatting and indentation preserved, except for
+the added leading space character in every line of text.
+
+
+AMD PowerNow! Drivers
+=====================
+
+::
+
+ PowerNow! and Cool'n'Quiet are AMD names for frequency
+ management capabilities in AMD processors. As the hardware
+ implementation changes in new generations of the processors,
+ there is a different cpu-freq driver for each generation.
+
+ Note that the driver's will not load on the "wrong" hardware,
+ so it is safe to try each driver in turn when in doubt as to
+ which is the correct driver.
+
+ Note that the functionality to change frequency (and voltage)
+ is not available in all processors. The drivers will refuse
+ to load on processors without this capability. The capability
+ is detected with the cpuid instruction.
+
+ The drivers use BIOS supplied tables to obtain frequency and
+ voltage information appropriate for a particular platform.
+ Frequency transitions will be unavailable if the BIOS does
+ not supply these tables.
+
+ 6th Generation: powernow-k6
+
+ 7th Generation: powernow-k7: Athlon, Duron, Geode.
+
+ 8th Generation: powernow-k8: Athlon, Athlon 64, Opteron, Sempron.
+ Documentation on this functionality in 8th generation processors
+ is available in the "BIOS and Kernel Developer's Guide", publication
+ 26094, in chapter 9, available for download from www.amd.com.
+
+ BIOS supplied data, for powernow-k7 and for powernow-k8, may be
+ from either the PSB table or from ACPI objects. The ACPI support
+ is only available if the kernel config sets CONFIG_ACPI_PROCESSOR.
+ The powernow-k8 driver will attempt to use ACPI if so configured,
+ and fall back to PST if that fails.
+ The powernow-k7 driver will try to use the PSB support first, and
+ fall back to ACPI if the PSB support fails. A module parameter,
+ acpi_force, is provided to force ACPI support to be used instead
+ of PSB support.
+
+
+``cpufreq-nforce2``
+===================
+
+::
+
+ The cpufreq-nforce2 driver changes the FSB on nVidia nForce2 platforms.
+
+ This works better than on other platforms, because the FSB of the CPU
+ can be controlled independently from the PCI/AGP clock.
+
+ The module has two options:
+
+ 	fid: 	 multiplier * 10 (for example 8.5 = 85)
+ 	min_fsb: minimum FSB
+
+ If not set, fid is calculated from the current CPU speed and the FSB.
+ min_fsb defaults to FSB at boot time - 50 MHz.
+
+ IMPORTANT: The available range is limited downwards!
+            Also the minimum available FSB can differ, for systems
+            booting with 200 MHz, 150 should always work.
+
+
+``pcc-cpufreq``
+===============
+
+::
+
+ /*
+  *  pcc-cpufreq.txt - PCC interface documentation
+  *
+  *  Copyright (C) 2009 Red Hat, Matthew Garrett <mjg@redhat.com>
+  *  Copyright (C) 2009 Hewlett-Packard Development Company, L.P.
+  *      Nagananda Chumbalkar <nagananda.chumbalkar@hp.com>
+  */
+
+
+ 			Processor Clocking Control Driver
+ 			---------------------------------
+
+ Contents:
+ ---------
+ 1.	Introduction
+ 1.1	PCC interface
+ 1.1.1	Get Average Frequency
+ 1.1.2	Set Desired Frequency
+ 1.2	Platforms affected
+ 2.	Driver and /sys details
+ 2.1	scaling_available_frequencies
+ 2.2	cpuinfo_transition_latency
+ 2.3	cpuinfo_cur_freq
+ 2.4	related_cpus
+ 3.	Caveats
+
+ 1. Introduction:
+ ----------------
+ Processor Clocking Control (PCC) is an interface between the platform
+ firmware and OSPM. It is a mechanism for coordinating processor
+ performance (ie: frequency) between the platform firmware and the OS.
+
+ The PCC driver (pcc-cpufreq) allows OSPM to take advantage of the PCC
+ interface.
+
+ OS utilizes the PCC interface to inform platform firmware what frequency the
+ OS wants for a logical processor. The platform firmware attempts to achieve
+ the requested frequency. If the request for the target frequency could not be
+ satisfied by platform firmware, then it usually means that power budget
+ conditions are in place, and "power capping" is taking place.
+
+ 1.1 PCC interface:
+ ------------------
+ The complete PCC specification is available here:
+ https://acpica.org/sites/acpica/files/Processor-Clocking-Control-v1p0.pdf
+
+ PCC relies on a shared memory region that provides a channel for communication
+ between the OS and platform firmware. PCC also implements a "doorbell" that
+ is used by the OS to inform the platform firmware that a command has been
+ sent.
+
+ The ACPI PCCH() method is used to discover the location of the PCC shared
+ memory region. The shared memory region header contains the "command" and
+ "status" interface. PCCH() also contains details on how to access the platform
+ doorbell.
+
+ The following commands are supported by the PCC interface:
+ * Get Average Frequency
+ * Set Desired Frequency
+
+ The ACPI PCCP() method is implemented for each logical processor and is
+ used to discover the offsets for the input and output buffers in the shared
+ memory region.
+
+ When PCC mode is enabled, the platform will not expose processor performance
+ or throttle states (_PSS, _TSS and related ACPI objects) to OSPM. Therefore,
+ the native P-state driver (such as acpi-cpufreq for Intel, powernow-k8 for
+ AMD) will not load.
+
+ However, OSPM remains in control of policy. The governor (eg: "ondemand")
+ computes the required performance for each processor based on server workload.
+ The PCC driver fills in the command interface, and the input buffer and
+ communicates the request to the platform firmware. The platform firmware is
+ responsible for delivering the requested performance.
+
+ Each PCC command is "global" in scope and can affect all the logical CPUs in
+ the system. Therefore, PCC is capable of performing "group" updates. With PCC
+ the OS is capable of getting/setting the frequency of all the logical CPUs in
+ the system with a single call to the BIOS.
+
+ 1.1.1 Get Average Frequency:
+ ----------------------------
+ This command is used by the OSPM to query the running frequency of the
+ processor since the last time this command was completed. The output buffer
+ indicates the average unhalted frequency of the logical processor expressed as
+ a percentage of the nominal (ie: maximum) CPU frequency. The output buffer
+ also signifies if the CPU frequency is limited by a power budget condition.
+
+ 1.1.2 Set Desired Frequency:
+ ----------------------------
+ This command is used by the OSPM to communicate to the platform firmware the
+ desired frequency for a logical processor. The output buffer is currently
+ ignored by OSPM. The next invocation of "Get Average Frequency" will inform
+ OSPM if the desired frequency was achieved or not.
+
+ 1.2 Platforms affected:
+ -----------------------
+ The PCC driver will load on any system where the platform firmware:
+ * supports the PCC interface, and the associated PCCH() and PCCP() methods
+ * assumes responsibility for managing the hardware clocking controls in order
+ to deliver the requested processor performance
+
+ Currently, certain HP ProLiant platforms implement the PCC interface. On those
+ platforms PCC is the "default" choice.
+
+ However, it is possible to disable this interface via a BIOS setting. In
+ such an instance, as is also the case on platforms where the PCC interface
+ is not implemented, the PCC driver will fail to load silently.
+
+ 2. Driver and /sys details:
+ ---------------------------
+ When the driver loads, it merely prints the lowest and the highest CPU
+ frequencies supported by the platform firmware.
+
+ The PCC driver loads with a message such as:
+ pcc-cpufreq: (v1.00.00) driver loaded with frequency limits: 1600 MHz, 2933
+ MHz
+
+ This means that the OPSM can request the CPU to run at any frequency in
+ between the limits (1600 MHz, and 2933 MHz) specified in the message.
+
+ Internally, there is no need for the driver to convert the "target" frequency
+ to a corresponding P-state.
+
+ The VERSION number for the driver will be of the format v.xy.ab.
+ eg: 1.00.02
+    ----- --
+     |    |
+     |    -- this will increase with bug fixes/enhancements to the driver
+     |-- this is the version of the PCC specification the driver adheres to
+
+
+ The following is a brief discussion on some of the fields exported via the
+ /sys filesystem and how their values are affected by the PCC driver:
+
+ 2.1 scaling_available_frequencies:
+ ----------------------------------
+ scaling_available_frequencies is not created in /sys. No intermediate
+ frequencies need to be listed because the BIOS will try to achieve any
+ frequency, within limits, requested by the governor. A frequency does not have
+ to be strictly associated with a P-state.
+
+ 2.2 cpuinfo_transition_latency:
+ -------------------------------
+ The cpuinfo_transition_latency field is 0. The PCC specification does
+ not include a field to expose this value currently.
+
+ 2.3 cpuinfo_cur_freq:
+ ---------------------
+ A) Often cpuinfo_cur_freq will show a value different than what is declared
+ in the scaling_available_frequencies or scaling_cur_freq, or scaling_max_freq.
+ This is due to "turbo boost" available on recent Intel processors. If certain
+ conditions are met the BIOS can achieve a slightly higher speed than requested
+ by OSPM. An example:
+
+ scaling_cur_freq	: 2933000
+ cpuinfo_cur_freq	: 3196000
+
+ B) There is a round-off error associated with the cpuinfo_cur_freq value.
+ Since the driver obtains the current frequency as a "percentage" (%) of the
+ nominal frequency from the BIOS, sometimes, the values displayed by
+ scaling_cur_freq and cpuinfo_cur_freq may not match. An example:
+
+ scaling_cur_freq	: 1600000
+ cpuinfo_cur_freq	: 1583000
+
+ In this example, the nominal frequency is 2933 MHz. The driver obtains the
+ current frequency, cpuinfo_cur_freq, as 54% of the nominal frequency:
+
+ 	54% of 2933 MHz = 1583 MHz
+
+ Nominal frequency is the maximum frequency of the processor, and it usually
+ corresponds to the frequency of the P0 P-state.
+
+ 2.4 related_cpus:
+ -----------------
+ The related_cpus field is identical to affected_cpus.
+
+ affected_cpus	: 4
+ related_cpus	: 4
+
+ Currently, the PCC driver does not evaluate _PSD. The platforms that support
+ PCC do not implement SW_ALL. So OSPM doesn't need to perform any coordination
+ to ensure that the same frequency is requested of all dependent CPUs.
+
+ 3. Caveats:
+ -----------
+ The "cpufreq_stats" module in its present form cannot be loaded and
+ expected to work with the PCC driver. Since the "cpufreq_stats" module
+ provides information wrt each P-state, it is not applicable to the PCC driver.