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authorDipen Patel <dipenp@nvidia.com>2022-04-22 13:52:14 -0700
committerThierry Reding <treding@nvidia.com>2022-05-04 11:06:13 +0200
commit09574cca6ad649f84ba804caf63a5aefe0202834 (patch)
treed1e3a6dc6f38428baa7c3a7de6fb4f3899534d91 /Documentation/hte
parent31ab09b4218879bc394c9faa6da983a82a694600 (diff)
downloadlwn-09574cca6ad649f84ba804caf63a5aefe0202834.tar.gz
lwn-09574cca6ad649f84ba804caf63a5aefe0202834.zip
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: Dipen Patel <dipenp@nvidia.com> Reported-by: kernel test robot <lkp@intel.com> Signed-off-by: Thierry Reding <treding@nvidia.com>
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-rw-r--r--Documentation/hte/index.rst22
-rw-r--r--Documentation/hte/tegra194-hte.rst49
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diff --git a/Documentation/hte/index.rst b/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
+
diff --git a/Documentation/hte/tegra194-hte.rst b/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.