Commit 09574cca authored by Dipen Patel's avatar Dipen Patel Committed by Thierry Reding
Browse files

hte: Add Tegra194 HTE kernel provider 



Tegra194 device has multiple HTE instances also known as GTE (Generic
Hardware Timestamping Engine) which can timestamp subset of SoC lines
and signals. This provider driver focuses on IRQ and GPIO lines and
exposes timestamping ability on those lines to the consumers through
HTE subsystem.

Also, with this patch, added:
- documentation about this provider and its capabilities at
Documentation/hte.
- Compilation support in Makefile and Kconfig

Signed-off-by: default avatarDipen Patel <dipenp@nvidia.com>
Reported-by: default avatarkernel test robot <lkp@intel.com>
Signed-off-by: default avatarThierry Reding <treding@nvidia.com>
parent 31ab09b4

Documentation/hte/index.rst

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.. 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

Documentation/hte/tegra194-hte.rst

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.. 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.



.. kernel-doc:: drivers/gpio/gpiolib.c

   :functions: gpiod_enable_hw_timestamp_ns 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/hte/``

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.

Documentation/index.rst

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@@ -139,6 +139,7 @@ needed). 
   mhi/index

   tty/index

   peci/index

   hte/index



Architecture-agnostic documentation

-----------------------------------

drivers/hte/Kconfig

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@@ -12,3 +12,15 @@ menuconfig HTE 


	  If unsure, say no.



if HTE



config HTE_TEGRA194

	tristate "NVIDIA Tegra194 HTE Support"

	depends on ARCH_TEGRA_194_SOC

	help

	  Enable this option for integrated hardware timestamping engine also

	  known as generic timestamping engine (GTE) support on NVIDIA Tegra194

	  systems-on-chip. The driver supports 352 LIC IRQs and 39 AON GPIOs

	  lines for timestamping in realtime.



endif

drivers/hte/Makefile

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obj-$(CONFIG_HTE)		+= hte.o

obj-$(CONFIG_HTE_TEGRA194)	+= hte-tegra194.o