Re: [PATCH v9 13/24] v4l: async: Allow async notifier register call succeed with no subdevs

[Hans Verkuil]

On 09/08/2017 03:18 PM, Sakari Ailus wrote:
> The information on how many async sub-devices would be bindable to a
> notifier is typically dependent on information from platform firmware and
> it's not driver's business to be aware of that.
> 
> Many V4L2 main drivers are perfectly usable (and useful) without async
> sub-devices and so if there aren't any around, just proceed call the
> notifier's complete callback immediately without registering the notifier
> itself.
> 
> If a driver needs to check whether there are async sub-devices available,
> it can be done by inspecting the notifier's num_subdevs field which tells
> the number of async sub-devices.
> 
> Signed-off-by: Sakari Ailus <sakari.ai...@linux.intel.com>
> ---
>  drivers/media/v4l2-core/v4l2-async.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-async.c 
> b/drivers/media/v4l2-core/v4l2-async.c
> index 7b396ff4302b..9ebc2e079d03 100644
> --- a/drivers/media/v4l2-core/v4l2-async.c
> +++ b/drivers/media/v4l2-core/v4l2-async.c
> @@ -170,10 +170,12 @@ int v4l2_async_notifier_register(struct v4l2_device 
> *v4l2_dev,
>       struct v4l2_async_subdev *asd;
>       int i;
>  
> -     if (!v4l2_dev || !notifier->num_subdevs ||
> -         notifier->num_subdevs > V4L2_MAX_SUBDEVS)
> +     if (!v4l2_dev || notifier->num_subdevs > V4L2_MAX_SUBDEVS)
>               return -EINVAL;
>  
> +     if (!notifier->num_subdevs)
> +             return v4l2_async_notifier_call_complete(notifier);
> +

I would move this 'if' down to after the next three lines...

>       notifier->v4l2_dev = v4l2_dev;
>       INIT_LIST_HEAD(&notifier->waiting);
>       INIT_LIST_HEAD(&notifier->done);
> 

...that way the notifier struct is properly initialized. Just in case anyone
ever looks at these three fields.

Regards,

        Hans