linux-kernel - Re: [PATCH v2 1/1] media: v4l: Don't turn on privacy LED if streamon fails

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Message-ID: <20240412174621.GA5444@pendragon.ideasonboard.com>
Date: Fri, 12 Apr 2024 20:46:21 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: linux-media@...r.kernel.org, tomi.valkeinen@...asonboard.com,
	Hans de Goede <hdegoede@...hat.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Hans Verkuil <hverkuil@...all.nl>,
	Umang Jain <umang.jain@...asonboard.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] media: v4l: Don't turn on privacy LED if streamon
 fails

Hi Sakari,

Thank you for the patch.

On Wed, Apr 10, 2024 at 02:47:12PM +0300, Sakari Ailus wrote:
> Turn on the privacy LED only if streamon succeeds. This can be done after
> enabling streaming on the sensor.
> 
> Fixes: b6e10ff6c23d ("media: v4l2-core: Make the v4l2-core code enable/disable the privacy LED if present")
> Signed-off-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> ---
>  drivers/media/v4l2-core/v4l2-subdev.c | 22 ++++++++++++----------
>  1 file changed, 12 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> index 4c6198c48dd6..012b757eac9f 100644
> --- a/drivers/media/v4l2-core/v4l2-subdev.c
> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> @@ -412,15 +412,6 @@ static int call_s_stream(struct v4l2_subdev *sd, int enable)
>  	if (WARN_ON(!!sd->enabled_streams == !!enable))
>  		return 0;
>  
> -#if IS_REACHABLE(CONFIG_LEDS_CLASS)
> -	if (!IS_ERR_OR_NULL(sd->privacy_led)) {
> -		if (enable)
> -			led_set_brightness(sd->privacy_led,
> -					   sd->privacy_led->max_brightness);
> -		else
> -			led_set_brightness(sd->privacy_led, 0);
> -	}
> -#endif
>  	ret = sd->ops->video->s_stream(sd, enable);
>  
>  	if (!enable && ret < 0) {
> @@ -428,9 +419,20 @@ static int call_s_stream(struct v4l2_subdev *sd, int enable)
>  		ret = 0;
>  	}
>  
> -	if (!ret)
> +	if (!ret) {
>  		sd->enabled_streams = enable ? BIT(0) : 0;
>  
> +#if IS_REACHABLE(CONFIG_LEDS_CLASS)
> +		if (!IS_ERR_OR_NULL(sd->privacy_led)) {
> +			if (enable)
> +				led_set_brightness(sd->privacy_led,
> +						   sd->privacy_led->max_brightness);
> +			else
> +				led_set_brightness(sd->privacy_led, 0);
> +		}
> +#endif

This means that the LED will be turned slightly after the camera is
enabled. I don't think it's an issue in practice. Another possibly more
important concern is that we should maybe check the return value of
led_set_brightness(), and fail .s_stream() when we can't enable the
privacy LED at stream on time. In that case, it would be best to keep
turning the privacy LED on before calling .s_stream(). It should still
be turned off only after calling .s_stream() though.

> +	}
> +
>  	return ret;
>  }
>  

-- 
Regards,

Laurent Pinchart