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

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Message-ID: <8d3257f3-54b1-e658-245d-3a070aba44c4@nvidia.com>
Date:   Tue, 3 Aug 2021 17:42:37 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Dipen Patel <dipenp@...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 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.

Jon

--
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