linux-kernel - Re: [PATCH v6 03/11] Documentation: uAPI: media: add V4L2_CID_FLASH

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Message-ID: <aKv3uUXf87im8ajX@kekkonen.localdomain>
Date: Mon, 25 Aug 2025 08:42:17 +0300
From: Sakari Ailus <sakari.ailus@...ux.intel.com>
To: Richard Leitner <richard.leitner@...ux.dev>
Cc: Dave Stevenson <dave.stevenson@...pberrypi.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Lee Jones <lee@...nel.org>, Pavel Machek <pavel@...nel.org>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Hans Verkuil <hverkuil@...all.nl>, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org
Subject: Re: [PATCH v6 03/11] Documentation: uAPI: media: add
 V4L2_CID_FLASH_DURATION

Hi Richard,

Thanks for the update (and for the ping!).

On Wed, Jul 16, 2025 at 11:06:53AM +0200, Richard Leitner wrote:
> Add the new strobe_duration control to v4l uAPI documentation.
> 
> Signed-off-by: Richard Leitner <richard.leitner@...ux.dev>
> ---
>  Documentation/userspace-api/media/v4l/ext-ctrls-flash.rst | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-flash.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-flash.rst
> index d22c5efb806a183a3ad67ec3e6550b002a51659a..03a58ef94be7c870f55d5a9bb09503995dbfb402 100644
> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-flash.rst
> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-flash.rst
> @@ -186,3 +186,8 @@ Flash Control IDs
>      charged before strobing. LED flashes often require a cooldown period
>      after strobe during which another strobe will not be possible. This
>      is a read-only control.
> +
> +``V4L2_CID_FLASH_DURATION (integer)``
> +    Duration the flash should be on when the flash LED is in flash mode
> +    (V4L2_FLASH_LED_MODE_FLASH). The unit should be microseconds (µs)
> +    if possible.
> 

I think we should add this is related to the hardware strobe.

How about:

``V4L2_CID_FLASH_DURATION (integer)``

    Duration of the flash strobe from the strobe source, typically a camera
    sensor. Controlling the flash LED strobe length this way requires that the
    flash LED driver's :ref:`flash LED mode <v4l2-cid-flash-led-mode>` is set
    to ``V4L2_FLASH_LED_MODE_FLASH`` and :ref:`strobe source
    <v4l2-cid-strobe-source>` is set to ``V4L2_FLASH_STROBE_SOURCE_EXTERNAL``.
    The unit should be microseconds (µs) if possible.

This requires of course the appropriate labels.

I also wonder whether we should use 0,1 µs or even ns for the unit.

-- 
Kind regards,

Sakari Ailus