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

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Message-ID: <0fd2cbfa-8804-456f-891d-ecd06e828bc6@xs4all.nl>
Date: Fri, 14 Mar 2025 11:36:12 +0100
From: Hans Verkuil <hverkuil@...all.nl>
To: Richard Leitner <richard.leitner@...ux.dev>
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

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.

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