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

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Message-ID: <20240415071812.GA25078@pendragon.ideasonboard.com>
Date: Mon, 15 Apr 2024 10:18:12 +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

On Mon, Apr 15, 2024 at 07:15:42AM +0000, Sakari Ailus wrote:
> Hi Laurent,
> 
> On Fri, Apr 12, 2024 at 08:46:21PM +0300, Laurent Pinchart wrote:
> > 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
> 
> That's what I'd think as well. Typically even the exposure time is much,
> much longer than what it takes to get here.
> 
> > 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.
> 
> The return type of led_set_brightness() is void.

Oops :-S

> Maybe because a large majority is GPIO-controlled?

GPIOs can fail, in particular when they're on I2C GPIO expanders.

-- 
Regards,

Laurent Pinchart