Re: [RFC v2 03/11] hte: Add tegra194 HTE kernel provider
From: Randy Dunlap <hidden>
Date: 2021-10-02 00:07:07
Also in:
linux-doc, linux-gpio, linux-tegra, lkml
On 9/30/21 4:26 PM, Dipen Patel wrote:
quoted hunk ↗ jump to hunk
diff --git a/Documentation/hte/tegra194-hte.rst b/Documentation/hte/tegra194-hte.rst new file mode 100644 index 000000000000..fb229bda2408 --- /dev/null +++ b/Documentation/hte/tegra194-hte.rst@@ -0,0 +1,56 @@ +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