linux-kernel - Re: [PATCH v2 4/8] Documentation: uAPI: media: add V4L2_CID_FLASH

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Message-ID: <p7dar3qvajkaq6y4mxahxh2g5vkxzavjjchkwvh32hhkptona2@mzgo4vf4ni7e>
Date: Tue, 25 Mar 2025 09:24:18 +0100
From: Richard Leitner <richard.leitner@...ux.dev>
To: Hans Verkuil <hverkuil@...all.nl>
Cc: Sakari Ailus <sakari.ailus@...ux.intel.com>, 
	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>, linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-leds@...r.kernel.org
Subject: Re: [PATCH v2 4/8] Documentation: uAPI: media: add
 V4L2_CID_FLASH_DURATION

Hi Hans, Hi Sakari,

On Fri, Mar 14, 2025 at 11:36:12AM +0100, Hans Verkuil wrote:
> On 14/03/2025 11:28, Richard Leitner wrote:
> > Hi Hans,
> > 
> > thanks for your quick feedback!
> > 
> > On Fri, Mar 14, 2025 at 10:41:04AM +0100, Hans Verkuil wrote:
> >> On 14/03/2025 09:49, 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.
> >>>
> >>
> >> If this control is present, does that mean that the flash duration always have
> >> to be set manually? Or can there be an 'Auto' mode as well? And if so, how is
> >> that set?
> > 
> > To be honest I haven't thought about automatic flash duration. Is this
> > something which is required?
> 
> No idea, it was just something I was wondering about. Sakari probably knows a lot
> more about this.

Sakari, should I add something like an auto/manual flash duration
control to this series?

Personally I think as long as we have no user of such an "auto" control
it's not really necessary. Or are there any drivers doing "auto"
flash/strobe duration already?

Thanks!

regards;rl

> 
> Regards,
> 
> 	Hans
> 
> > 
> > At least for the ov9282 sensor (which I've implemented this control for
> > in this series) there is no "auto" mode AFAIK.
> > 
> > If it's required: What would be the best solution?
> > Extending V4L2_CID_FLASH_LED_MODE with a new menu option? E.g.
> > V4L2_FLASH_LED_MODE_FLASH_{MANUAL,AUTO}?
> > 
> >>
> >> Regards,
> >>
> >> 	Hans
> > 
> > Thanks!
> > Richard
>