Re: [PATCH v10 05/38] media: subdev: Add v4l2_subdev_lock_and_return_state()

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Tomi,

Thank you for the patch.

On Tue, Nov 30, 2021 at 04:15:03PM +0200, Tomi Valkeinen wrote:
> All suitable subdev ops are now passed either the TRY or the ACTIVE
> state by the v4l2 core. However, other subdev drivers can still call the
> ops passing NULL as the state, implying the active case.
> 
> For all current upstream drivers this doesn't matter, as they do not
> expect to get a valid state for ACTIVE case. But future drivers which
> support multiplexed streaming and routing will depend on getting a state
> for both active and try cases.
> 
> For new drivers we can mandate that the pipelines where the drivers are
> used need to pass the state properly, or preferably, not call such
> subdev ops at all.
> 
> However, if an existing subdev driver is changed to support multiplexed
> streams, the driver has to consider cases where its ops will be called
> with NULL state. The problem can easily be solved by using the
> v4l2_subdev_lock_and_return_state() helper, introduced here.
> 
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
> ---
>  include/media/v4l2-subdev.h | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
> 
> diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
> index 1810dde9c7fc..873bbe0686e3 100644
> --- a/include/media/v4l2-subdev.h
> +++ b/include/media/v4l2-subdev.h
> @@ -1317,4 +1317,35 @@ void v4l2_subdev_lock_state(struct v4l2_subdev_state *state);
>   */
>  void v4l2_subdev_unlock_state(struct v4l2_subdev_state *state);
>  
> +/**
> + * v4l2_subdev_lock_and_return_state() - Gets locked TRY or ACTIVE subdev state
> + * @sd: subdevice
> + * @state: subdevice state as passed to the subdev op
> + *
> + * Due to legacy reasons, when subdev drivers call ops in other subdevs they use
> + * NULL as the state parameter, as subdevs always used to have their active
> + * state stored privately.
> + *
> + * However, newer state-aware subdev drivers, which store their active state in
> + * a common place, subdev->active_state, expect to always get a proper state as
> + * a parameter.
> + *
> + * These state-aware drivers can use v4l2_subdev_lock_and_return_state() instead
> + * of v4l2_subdev_lock_state(). v4l2_subdev_lock_and_return_state() solves the
> + * issue by using subdev->state in case the passed state is NULL.
> + *
> + * This is a temporary helper function, and should be removed when we can ensure
> + * that all drivers pass proper state when calling other subdevs.
> + */
> +static inline struct v4l2_subdev_state *
> +v4l2_subdev_lock_and_return_state(struct v4l2_subdev *sd,
> +				  struct v4l2_subdev_state *state)
> +{
> +	state = state ? state : sd->active_state;

Can we add a dev_warn() when state is NULL ? This will help speeding up
the transition.

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

> +
> +	v4l2_subdev_lock_state(state);
> +
> +	return state;
> +}
> +
>  #endif

-- 
Regards,

Laurent Pinchart