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

Hans Verkuil
2017-09-11T08:05:45Z

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.ailus@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