linux-kernel - Re: [RFC v2 03/11] hte: Add tegra194 HTE kernel provider

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Date:   Tue, 2 Nov 2021 18:15:56 -0700
From:   Dipen Patel <dipenp@...dia.com>
To:     Randy Dunlap <rdunlap@...radead.org>, <thierry.reding@...il.com>,
        <jonathanh@...dia.com>, <linux-kernel@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>, <linux-gpio@...r.kernel.org>,
        <linus.walleij@...aro.org>, <bgolaszewski@...libre.com>,
        <warthog618@...il.com>, <devicetree@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <robh+dt@...nel.org>
Subject: Re: [RFC v2 03/11] hte: Add tegra194 HTE kernel provider

Hi Randy,

Thanks for the comments. I will implement changes in RFC V3.

Best Regards,

Dipen Patel

On 10/1/21 5:07 PM, Randy Dunlap wrote:
> 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``.
>> +
>
>