linux-kernel - Re: [RFC 08/11] gpiolib: cdev: Add hardware timestamp clock type

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Message-ID: <f0d8da75-6e31-5432-6909-8eab6960b787@nvidia.com>
Date:   Tue, 3 Aug 2021 15:51:31 -0700
From:   Dipen Patel <dipenp@...dia.com>
To:     Jon Hunter <jonathanh@...dia.com>, <thierry.reding@...il.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 08/11] gpiolib: cdev: Add hardware timestamp clock type


On 8/3/21 9:42 AM, Jon Hunter wrote:
>
> On 30/07/2021 03:33, Dipen Patel wrote:
>>
>> On 7/9/21 1:30 AM, Jon Hunter wrote:
>>> On 26/06/2021 00:55, Dipen Patel wrote:
>>>> This patch adds new clock type for the GPIO controller which can
>>>> timestamp gpio lines using hardware means. To expose such
>>>> functionalities to the userspace, code has been added in this patch
>>>> where during line create call, it checks for new clock type and if
>>>> requested, calls hardware timestamp related API from gpiolib.c.
>>>> During line change event, it retrieves timestamp in nano seconds by
>>>> calling gpiod_get_hw_timestamp API from gpiolib.c. At the line release,
>>>> it disables this functionality by calling gpiod_hw_timestamp_control.
>>>>
>>>> Signed-off-by: Dipen Patel <dipenp@...dia.com>
>>>> ---
>>>>   drivers/gpio/gpiolib-cdev.c | 65 +++++++++++++++++++++++++++++++++++--
>>>>   include/uapi/linux/gpio.h   |  1 +
>>>>   2 files changed, 64 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
>>>> index 1631727bf0da..9f98c727e937 100644
>>>> --- a/drivers/gpio/gpiolib-cdev.c
>>>> +++ b/drivers/gpio/gpiolib-cdev.c
>>>> @@ -518,6 +518,7 @@ struct linereq {
>>>>        GPIO_V2_LINE_DRIVE_FLAGS | \
>>>>        GPIO_V2_LINE_EDGE_FLAGS | \
>>>>        GPIO_V2_LINE_FLAG_EVENT_CLOCK_REALTIME | \
>>>> +     GPIO_V2_LINE_FLAG_EVENT_CLOCK_HARDWARE | \
>>>>        GPIO_V2_LINE_BIAS_FLAGS)
>>>>     static void linereq_put_event(struct linereq *lr,
>>>> @@ -540,9 +541,20 @@ static void linereq_put_event(struct linereq *lr,
>>>>     static u64 line_event_timestamp(struct line *line)
>>>>   {
>>>> +    bool block;
>>>> +
>>>>       if (test_bit(FLAG_EVENT_CLOCK_REALTIME, &line->desc->flags))
>>>>           return ktime_get_real_ns();
>>>>   +    if (test_bit(FLAG_EVENT_CLOCK_HARDWARE, &line->desc->flags)) {
>>>> +        if (irq_count())
>>>> +            block = false;
>>>> +        else
>>>> +            block = true;
>>>> +
>>>> +        return gpiod_get_hw_timestamp(line->desc, block);
>>>> +    }
>>>> +
>>>>       return ktime_get_ns();
>>>>   }
>>>
>>> Looking at line_event_timestamp() and the callers of this function, it
>>> appears that this should always return nanoseconds. Does
>>> gpiod_get_hw_timestamp() return nanoseconds?
>> Yes, it returns in ns to align with line_event_timestamp.
>
>
> It might be worth updating the function name to gpiod_get_hw_timestamp_ns() so that this is clear.
Wouldn't be sufficient to right into its description rather embed in API name?
>
> Jon
>
> -- 
> nvpublic