linux-kernel - Re: [PATCH] media: v4l2-subdev: Refactor events

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Message-ID: <20241020154638.GC7770@pendragon.ideasonboard.com>
Date: Sun, 20 Oct 2024 18:46:38 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: Tommaso Merciai <tomm.merciai@...il.com>, prabhakar.csengg@...il.com,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Hans Verkuil <hverkuil@...all.nl>,
	Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
	Paweł Anikiel <panikiel@...gle.com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: v4l2-subdev: Refactor events

On Sun, Oct 20, 2024 at 10:45:59AM +0000, Sakari Ailus wrote:
> Hi Tommaso,
> 
> On Sun, Oct 20, 2024 at 12:07:19AM +0200, Tommaso Merciai wrote:
> > Hi Sakari,
> > 
> > On Fri, Oct 18, 2024 at 07:30:30PM +0000, Sakari Ailus wrote:
> > > Hi Tommaso,
> > > 
> > > Thanks for working on this.
> > 
> > In real it's a Laurent's suggestion :)
> > 
> > > 
> > > On Fri, Oct 18, 2024 at 07:11:03PM +0200, Tommaso Merciai wrote:
> > > > Controls can be exposed to userspace via a v4l-subdevX device, and
> > > > userspace has to be able to subscribe to control events so that it is
> > > > notified when the control changes value.
> > > > If a control handler is set for the subdev then set the HAS_EVENTS
> > > > flag automatically into v4l2_subdev_init_finalize() and use
> > > > v4l2_ctrl_subdev_subscribe_event() and v4l2_event_subdev_unsubscribe()
> > > > as default if subdev don't have .(un)subscribe control operations.
> > > > 
> > > > Signed-off-by: Tommaso Merciai <tomm.merciai@...il.com>
> > > > ---
> > > >  drivers/media/v4l2-core/v4l2-subdev.c | 22 ++++++++++++++++++++--
> > > >  1 file changed, 20 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> > > > index 3a4ba08810d2..77ca829b9983 100644
> > > > --- a/drivers/media/v4l2-core/v4l2-subdev.c
> > > > +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> > > > @@ -691,10 +691,25 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
> > > >  		return v4l2_event_dequeue(vfh, arg, file->f_flags & O_NONBLOCK);
> > > >  
> > > >  	case VIDIOC_SUBSCRIBE_EVENT:
> > > > -		return v4l2_subdev_call(sd, core, subscribe_event, vfh, arg);
> > > > +		if (v4l2_subdev_has_op(sd, core, subscribe_event))
> > > > +			return v4l2_subdev_call(sd, core, subscribe_event,
> > > > +						vfh, arg);
> > > > +
> > > > +		if ((sd->flags & V4L2_SUBDEV_FL_HAS_EVENTS) &&
> > > > +		     vfh->ctrl_handler)
> > > > +			return v4l2_ctrl_subdev_subscribe_event(sd, vfh, arg);
> > > > +
> > > > +		return -ENOIOCTLCMD;
> > > 
> > > While this mostly does the same thing, I prefer the order of tests below.
> > > Could you align event subscription with unsubscription?
> > 
> > What about:
> > 
> > 	case VIDIOC_SUBSCRIBE_EVENT:
> > 		if (!(sd->flags & V4L2_SUBDEV_FL_HAS_EVENTS))
> > 			return -ENOIOCTLCMD;
> > 
> > 		if (v4l2_subdev_has_op(sd, core, subscribe_event))
> > 			return v4l2_subdev_call(sd, core, subscribe_event,
> > 						vfh, arg);
> > 
> > 		if (!vfh->ctrl_handler)
> > 			return -ENOTTY;
> > 
> > 		return v4l2_ctrl_subdev_subscribe_event(sd, vfh, arg);
> 
> Oh, right. Actually the earlier unsubscription didn't always produce
> correct results. I missed that. This is needlessly complicated at the
> moment. So I'd do:
> 
> 	case VIDIOC_SUBSCRIBE_EVENT:
> 		if (v4l2_subdev_has_op(sd, core, subscribe_event))
> 			return v4l2_subdev_call(sd, core, subscribe_event,
> 						vfh, arg);
> 
> 		return (sd->flags & V4L2_SUBDEV_FL_HAS_EVENTS) &&
> 			vfh->ctrl_handler ?
> 			v4l2_ctrl_subdev_subscribe_event(sd, vfh, arg) :
> 			-ENOIOCTLCMD;

Let's make this clearer:


		if (sd->flags & V4L2_SUBDEV_FL_HAS_EVENTS) &&
		    vfh->ctrl_handler)
			return v4l2_ctrl_subdev_subscribe_event(sd, vfh, arg);

		return -ENOIOCTLCMD;

> 
> 	case VIDIOC_UNSUBSCRIBE_EVENT:
> 		if (v4l2_subdev_has_op(sd, core, unsubscribe_event))
> 			return v4l2_subdev_call(sd, core, unsubscribe_event,
> 						vfh, arg);
> 
> 		return sd->flags & V4L2_SUBDEV_FL_HAS_EVENTS ?
> 			v4l2_event_subdev_unsubscribe(sd, vfh, arg) :
> 			-ENOIOCTLCMD;

		if (sd->flags & V4L2_SUBDEV_FL_HAS_EVENTS)
			return v4l2_event_subdev_unsubscribe(sd, vfh, arg);

		return -ENOIOCTLCMD;

> 
> 
> > 
> > 	case VIDIOC_UNSUBSCRIBE_EVENT:
> > 		if (!(sd->flags & V4L2_SUBDEV_FL_HAS_EVENTS))
> > 			return -ENOIOCTLCMD;
> > 
> > 		if (v4l2_subdev_has_op(sd, core, unsubscribe_event))
> > 			return v4l2_subdev_call(sd, core, unsubscribe_event,
> > 						vfh, arg);
> > 
> > 		return v4l2_event_subdev_unsubscribe(sd, vfh, arg);
> > 
> > ?
> > 
> > > >  
> > > >  	case VIDIOC_UNSUBSCRIBE_EVENT:
> > > > -		return v4l2_subdev_call(sd, core, unsubscribe_event, vfh, arg);
> > > > +		if (!(sd->flags & V4L2_SUBDEV_FL_HAS_EVENTS))
> > > > +			return -ENOIOCTLCMD;
> > > > +
> > > > +		if (v4l2_subdev_has_op(sd, core, unsubscribe_event))
> > > > +			return v4l2_subdev_call(sd, core, unsubscribe_event,
> > > > +						vfh, arg);
> > > > +
> > > > +		return v4l2_event_subdev_unsubscribe(sd, vfh, arg);
> > > >  
> > > >  #ifdef CONFIG_VIDEO_ADV_DEBUG
> > > >  	case VIDIOC_DBG_G_REGISTER:
> > > > @@ -1641,6 +1656,9 @@ int __v4l2_subdev_init_finalize(struct v4l2_subdev *sd, const char *name,
> > > >  		}
> > > >  	}
> > > >  
> > > > +	if (sd->ctrl_handler)
> > > > +		sd->flags |= V4L2_SUBDEV_FL_HAS_EVENTS;
> > > > +
> > > >  	state = __v4l2_subdev_state_alloc(sd, name, key);
> > > >  	if (IS_ERR(state))
> > > >  		return PTR_ERR(state);

-- 
Regards,

Laurent Pinchart