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| -rw-r--r-- | Documentation/driver-api/hte/hte.rst | 79 | ||||
| -rw-r--r-- | Documentation/driver-api/hte/index.rst | 22 | ||||
| -rw-r--r-- | Documentation/driver-api/hte/tegra194-hte.rst | 48 |
3 files changed, 149 insertions, 0 deletions
diff --git a/Documentation/driver-api/hte/hte.rst b/Documentation/driver-api/hte/hte.rst new file mode 100644 index 000000000..153f3233c --- /dev/null +++ b/Documentation/driver-api/hte/hte.rst @@ -0,0 +1,79 @@ +.. SPDX-License-Identifier: GPL-2.0+ + +============================================ +The Linux Hardware Timestamping Engine (HTE) +============================================ + +:Author: Dipen Patel + +Introduction +------------ + +Certain devices have built in hardware timestamping engines which can +monitor sets of system signals, lines, buses etc... in realtime for state +change; upon detecting the change they can automatically store the timestamp at +the moment of occurrence. Such functionality may help achieve better accuracy +in obtaining timestamps than using software counterparts i.e. ktime and +friends. + +This document describes the API that can be used by hardware timestamping +engine provider and consumer drivers that want to use the hardware timestamping +engine (HTE) framework. Both consumers and providers must include +``#include <linux/hte.h>``. + +The HTE framework APIs for the providers +---------------------------------------- + +.. kernel-doc:: drivers/hte/hte.c + :functions: devm_hte_register_chip hte_push_ts_ns + +The HTE framework APIs for the consumers +---------------------------------------- + +.. kernel-doc:: drivers/hte/hte.c + :functions: hte_init_line_attr hte_ts_get hte_ts_put devm_hte_request_ts_ns hte_request_ts_ns hte_enable_ts hte_disable_ts of_hte_req_count hte_get_clk_src_info + +The HTE framework public structures +----------------------------------- +.. kernel-doc:: include/linux/hte.h + +More on the HTE timestamp data +------------------------------ +The ``struct hte_ts_data`` is used to pass timestamp details between the +consumers and the providers. It expresses timestamp data in nanoseconds in +u64. An example of the typical timestamp data life cycle, for the GPIO line is +as follows:: + + - Monitors GPIO line change. + - Detects the state change on GPIO line. + - Converts timestamps in nanoseconds. + - Stores GPIO raw level in raw_level variable if the provider has that + hardware capability. + - Pushes this hte_ts_data object to HTE subsystem. + - HTE subsystem increments seq counter and invokes consumer provided callback. + Based on callback return value, the HTE core invokes secondary callback in + the thread context. + +HTE subsystem debugfs attributes +-------------------------------- +HTE subsystem creates debugfs attributes at ``/sys/kernel/debug/hte/``. +It also creates line/signal-related debugfs attributes at +``/sys/kernel/debug/hte/<provider>/<label or line id>/``. Note that these +attributes are read-only. + +`ts_requested` + The total number of entities requested from the given provider, + where entity is specified by the provider and could represent + lines, GPIO, chip signals, buses etc... + The attribute will be available at + ``/sys/kernel/debug/hte/<provider>/``. + +`total_ts` + The total number of entities supported by the provider. + The attribute will be available at + ``/sys/kernel/debug/hte/<provider>/``. + +`dropped_timestamps` + The dropped timestamps for a given line. + The attribute will be available at + ``/sys/kernel/debug/hte/<provider>/<label or line id>/``. diff --git a/Documentation/driver-api/hte/index.rst b/Documentation/driver-api/hte/index.rst new file mode 100644 index 000000000..9f43301c0 --- /dev/null +++ b/Documentation/driver-api/hte/index.rst @@ -0,0 +1,22 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================================ +The Linux Hardware Timestamping Engine (HTE) +============================================ + +The HTE Subsystem +================= + +.. toctree:: + :maxdepth: 1 + + hte + +HTE Tegra Provider +================== + +.. toctree:: + :maxdepth: 1 + + tegra194-hte + diff --git a/Documentation/driver-api/hte/tegra194-hte.rst b/Documentation/driver-api/hte/tegra194-hte.rst new file mode 100644 index 000000000..f2d617265 --- /dev/null +++ b/Documentation/driver-api/hte/tegra194-hte.rst @@ -0,0 +1,48 @@ +.. SPDX-License-Identifier: GPL-2.0+ + +HTE Kernel provider driver +========================== + +Description +----------- +The Nvidia tegra194 HTE provider driver implements two GTE +(Generic Timestamping Engine) instances: 1) GPIO GTE and 2) LIC +(Legacy Interrupt Controller) IRQ GTE. Both GTE instances get the +timestamp from the system counter TSC which has 31.25MHz clock rate, and the +driver converts clock tick rate to nanoseconds before storing it as timestamp +value. + +GPIO GTE +-------- + +This GTE instance timestamps GPIO in real time. For that to happen GPIO +needs to be configured as input. The always on (AON) GPIO controller instance +supports timestamping GPIOs in real time and it has 39 GPIO lines. The GPIO GTE +and AON GPIO controller are tightly coupled as it requires very specific bits +to be set in GPIO config register before GPIO GTE can be used, for that GPIOLIB +adds two optional APIs as below. The GPIO GTE code supports both kernel +and userspace consumers. The kernel space consumers can directly talk to HTE +subsystem while userspace consumers timestamp requests go through GPIOLIB CDEV +framework to HTE subsystem. + +See gpiod_enable_hw_timestamp_ns() and gpiod_disable_hw_timestamp_ns(). + +For userspace consumers, GPIO_V2_LINE_FLAG_EVENT_CLOCK_HTE flag must be +specified during IOCTL calls. Refer to ``tools/gpio/gpio-event-mon.c``, which +returns the timestamp in nanoseconds. + +LIC (Legacy Interrupt Controller) IRQ GTE +----------------------------------------- + +This GTE instance timestamps LIC IRQ lines in real time. There are 352 IRQ +lines which this instance can add timestamps to in real time. The hte +devicetree binding described at ``Documentation/devicetree/bindings/timestamp`` +provides an example of how a consumer can request an IRQ line. Since it is a +one-to-one mapping with IRQ GTE provider, consumers can simply specify the IRQ +number that they are interested in. There is no userspace consumer support for +this GTE instance in the HTE framework. + +The provider source code of both IRQ and GPIO GTE instances is located at +``drivers/hte/hte-tegra194.c``. The test driver +``drivers/hte/hte-tegra194-test.c`` demonstrates HTE API usage for both IRQ +and GPIO GTE. |