Re: [PATCH v2] media: v4l2-subdev: Refactor events

[Laurent Pinchart]

Hi Tommaso,

Thank you for the patch.

On Sun, Oct 20, 2024 at 06:35:32PM +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.

I would add here

This simplifies subdev drivers by avoiding the need to set the
V4L2_SUBDEV_FL_HAS_EVENTS flag and plug the event handlers, and ensures
consistency of the API exposed to userspace.

And you can also add

Suggested-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>

> Signed-off-by: Tommaso Merciai <tomm.merciai@xxxxxxxxx>

Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>

Now, can we simplify sensor drivers to drop the event handlers and the
flag ? :-)

> ---
> Changes since v1:
>  - Aligned event subscription with unsubscription as suggested by LPinchart,
>    SAilus
> 
>  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..fad8fa1f63e8 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;
>  
>  	case VIDIOC_UNSUBSCRIBE_EVENT:
> -		return v4l2_subdev_call(sd, core, unsubscribe_event, vfh, arg);
> +		if (v4l2_subdev_has_op(sd, core, unsubscribe_event))
> +			return v4l2_subdev_call(sd, core, unsubscribe_event,
> +						vfh, arg);
> +
> +		if (sd->flags & V4L2_SUBDEV_FL_HAS_EVENTS)
> +			return v4l2_event_subdev_unsubscribe(sd, vfh, arg);
> +
> +		return -ENOIOCTLCMD;
>  
>  #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