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    SubjectRe: [RFC v2 03/11] hte: Add tegra194 HTE kernel provider
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    Date
    On 9/30/21 4:26 PM, Dipen Patel wrote:
    > 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

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