On 9/30/21 4:26 PM, Dipen Patel wrote:
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+HTE Kernel provider driver
+==========================
+
+Description
+-----------
+The Nvidia tegra194 HTE provider driver implements two GTE
+(Generic Timestamping Engine) instances 1) GPIO GTE and 2) LIC IRQ GTE. The
instances: ^^Drop "The"
+both GTEs instances get the timestamp from the system counter TSC which has
Both
+31.25MHz clock rate, and the driver converts clock tick rate to nano seconds
nanoseconds
+before storing it as timestamp value.
+
+GPIO GTE
+--------
+
+This GTE instance timestamps GPIO in real time, for that to happen GPIO
time. For
+needs to be configured as input and IRQ needs to ba enabled. The only always on
be
+(AON) gpio controller instance supports timestamping GPIOs in realtime and it
GPIO real time {or change
the instance 3 lines above to be "realtime"}
+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. The GPIO GTE functionality is accessed from the GPIOLIB
+framework for the in kernel and userspace consumers. In the later case,
in-kernel latter
+requests go through GPIOLIB CDEV framework. The below APIs are added in GPIOLIB
+framework to access HTE subsystem and GPIO GTE.
+
+.. kernel-doc:: drivers/gpio/gpiolib.c
+ :functions: gpiod_req_hw_timestamp_ns gpiod_rel_hw_timestamp_ns
+
+There is hte-tegra194-gpio-test.c, located in ``drivers/hte/`` directory, test
+driver which demonstrates above APIs for the Jetson AGX platform.
+
+For userspace consumers, GPIO_V2_LINE_FLAG_EVENT_CLOCK_HARDWARE flag must be
+specifed during IOCTL calls, refer ``tools/gpio/gpio-event-mon.c``, which
specified calls. Refer to
+returns the timestamp in nano second.
nanoseconds.
+
+LIC IRQ GTE
+-----------
+
+This GTE instance timestamp LIC IRQ lines in real time. There are 352 IRQ
timestamps ^^^^^^^^^ {be consistent}
(also (repeating a prior email) define "LIC")
+lines which this instance can help timestamp realtime. The hte devicetree
can add timestamps to in realtime.
+binding described at ``Documentation/devicetree/bindings/hte/`` gives out
provides an
+example how consumer can request IRQ line, since it is one to one mapping,
example of how a consumer can request an IRQ line. Since it is a one-to-one mapping,
+consumers can simply specify IRQ number that they are interested in. There is
specify the IRQ number
+no userspace consumer support for this GTE instance. The sample test code
+hte-tegra194-irq-test.c, located in ``drivers/hte/`` directory,
in the
+demonstrates how to use IRQ GTE instance. The below is sample device tree
how to use an IRQ GTE instance.
+snippet code for the test driver::
+
+ tegra_hte_irq_test {
+ compatible = "nvidia,tegra194-hte-irq-test";
+ htes = <&tegra_hte_lic 0x19>;
+ hte-names = "hte-lic";
+ };
+
+The provider source code of both IRQ and GPIO GTE instances is locate at
located
+``drivers/hte/hte-tegra194.c``.
+
--
~Randy
