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

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Message-ID: <7e49e6a9-bd7c-1b97-50e6-bc803addc27f@nvidia.com>
Date:   Fri, 9 Jul 2021 09:30:52 +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 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?

Jon

-- 
nvpublic