linux-kernel - Re: [PATCH v7 02/10] media: v4l2-flash: add support for flash/strobe duration

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Message-ID: <20250907190520.GB4105@pendragon.ideasonboard.com>
Date: Sun, 7 Sep 2025 21:05:20 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
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>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-leds@...r.kernel.org, Hans Verkuil <hverkuil@...nel.org>
Subject: Re: [PATCH v7 02/10] media: v4l2-flash: add support for flash/strobe
 duration

Hi Richard,

Thank you for the patch.

On Mon, Sep 01, 2025 at 05:05:07PM +0200, Richard Leitner wrote:
> Add support for the new V4L2_CID_FLASH_DURATION control to the v4l2
> flash led class.

I don't think this is a good idea, based on the reasoning explained in
the review of 01/10. If V4L2_CID_FLASH_DURATION is meant to indicate the
duration of the external flash/strobe pulse signal, it should be
implemented by the source of the signal, and for external strobe mode
only. The flash controller, which receives the flash/strobe pulse,
should implement the timeout control.

> Signed-off-by: Richard Leitner <richard.leitner@...ux.dev>
> ---
>  drivers/media/v4l2-core/v4l2-flash-led-class.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-flash-led-class.c b/drivers/media/v4l2-core/v4l2-flash-led-class.c
> index 355595a0fefac72c2f6941a30fa430d37dbdccfe..875d56d7190592c1e5ab7acd617b76dcec8792da 100644
> --- a/drivers/media/v4l2-core/v4l2-flash-led-class.c
> +++ b/drivers/media/v4l2-core/v4l2-flash-led-class.c
> @@ -29,6 +29,7 @@ enum ctrl_init_data_id {
>  	INDICATOR_INTENSITY,
>  	FLASH_TIMEOUT,
>  	STROBE_SOURCE,
> +	FLASH_DURATION,
>  	/*
>  	 * Only above values are applicable to
>  	 * the 'ctrls' array in the struct v4l2_flash.
> @@ -298,6 +299,12 @@ static int v4l2_flash_s_ctrl(struct v4l2_ctrl *c)
>  		 * microamperes for flash intensity units.
>  		 */
>  		return led_set_flash_brightness(fled_cdev, c->val);
> +	case V4L2_CID_FLASH_DURATION:
> +		/*
> +		 * No conversion is needed as LED Flash class also uses
> +		 * microseconds for flash duration units.
> +		 */
> +		return led_set_flash_duration(fled_cdev, c->val);
>  	}
>  
>  	return -EINVAL;
> @@ -424,6 +431,14 @@ static void __fill_ctrl_init_data(struct v4l2_flash *v4l2_flash,
>  		ctrl_cfg->flags = V4L2_CTRL_FLAG_VOLATILE |
>  				  V4L2_CTRL_FLAG_EXECUTE_ON_WRITE;
>  	}
> +
> +	/* Init FLASH_DURATION ctrl data */
> +	if (has_flash_op(fled_cdev, duration_set)) {
> +		ctrl_init_data[FLASH_DURATION].cid = V4L2_CID_FLASH_DURATION;
> +		ctrl_cfg = &ctrl_init_data[FLASH_DURATION].config;
> +		__lfs_to_v4l2_ctrl_config(&fled_cdev->duration, ctrl_cfg);
> +		ctrl_cfg->id = V4L2_CID_FLASH_DURATION;
> +	}
>  }
>  
>  static int v4l2_flash_init_controls(struct v4l2_flash *v4l2_flash,
> @@ -543,6 +558,16 @@ static int __sync_device_with_v4l2_controls(struct v4l2_flash *v4l2_flash)
>  			return ret;
>  	}
>  
> +	if (ctrls[FLASH_DURATION]) {
> +		if (WARN_ON_ONCE(!fled_cdev))
> +			return -EINVAL;
> +
> +		ret = led_set_flash_duration(fled_cdev,
> +					     ctrls[FLASH_DURATION]->val);
> +		if (ret < 0)
> +			return ret;
> +	}
> +
>  	/*
>  	 * For some hardware arrangements setting strobe source may affect
>  	 * torch mode. Synchronize strobe source setting only if not in torch

-- 
Regards,

Laurent Pinchart