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

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Date:   Thu, 29 Jul 2021 19:33:29 -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 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.
>
> Jon
>