Re: [PATCH] drm/atomic: Add __drm_atomic_get_current_plane_state

[Eric Engestrom <eric.engestrom@imgtec.com>]

On Thu, Jun 02, 2016 at 04:21:44PM +0200, Daniel Vetter wrote:
> ... and use it in msm&vc4. Again just want to encapsulate
> drm_atomic_state internals a bit.
> 
> The const threading is a bit awkward in vc4 since C sucks, but I still
> think it's worth to enforce this. Eventually I want to make all the
> obj->state pointers const too, but that's a lot more work ...
> 
> v2: Provide safe macro to wrap up the unsafe helper better, suggested
> by Maarten.
> 
> Cc: Eric Anholt <eric@anholt.net>
> Cc: Rob Clark <robdclark@gmail.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  drivers/gpu/drm/msm/mdp/mdp5/mdp5_crtc.c | 10 ++-------
>  drivers/gpu/drm/vc4/vc4_crtc.c           | 13 ++----------
>  drivers/gpu/drm/vc4/vc4_drv.h            |  2 +-
>  drivers/gpu/drm/vc4/vc4_plane.c          |  5 +++--
>  include/drm/drm_atomic.h                 | 36 ++++++++++++++++++++++++++++++++
>  include/drm/drm_atomic_helper.h          | 24 +++++++++++++++++++--
>  6 files changed, 66 insertions(+), 24 deletions(-)

[...]

> diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> index 92c84e9ab09a..4e97186293be 100644
> --- a/include/drm/drm_atomic.h
> +++ b/include/drm/drm_atomic.h
> @@ -109,6 +109,42 @@ drm_atomic_get_existing_connector_state(struct drm_atomic_state *state,
>  	return state->connector_states[index];
>  }
>  
> +/**
> + * __drm_atomic_get_current_plane_state - get current plane state
> + * @state: global atomic state object
> + * @plane: plane to grab
> + *
> + * This function returns the plane state for the given plane, either from
> + * @state, or if the plane isn't part of the atomic state update, from @plane.
> + * This is useful in atomic check callbacks, when drivers need to peek at, but
> + * not change, state of other planes, since it avoids threading an error code
> + * back up the call chain.
> + *
> + * WARNING:
> + *
> + * Note that this function is in general unsafe since it doesn't check for the
> + * required locking for access state structures. Drivers must ensure that it is
> + * save to access the returned state structure through other means. One commone

s/save/safe/
s/commone/common/

> + * example is when planes are fixed to a single CRTC, and the driver knows that
> + * the CRTC locks is held already. In that case holding the CRTC locks gives a
> + * read-lock on all planes connected to that CRTC. But if planes can be
> + * reassigned things get more tricky. In that case it's better to use
> + * drm_atomic_get_plane_state and wire up full error handling.
> + *
> + * Returns:
> + *
> + * Read-only pointer to the current plane state.
> + */
> +static inline const struct drm_plane_state *
> +__drm_atomic_get_current_plane_state(struct drm_atomic_state *state,
> +				     struct drm_plane *plane)
> +{
> +	if (state->plane_states[drm_plane_index(plane)])
> +		return state->plane_states[drm_plane_index(plane)];
> +
> +	return plane->state;
> +}
> +
>  int __must_check
>  drm_atomic_set_mode_for_crtc(struct drm_crtc_state *state,
>  			     struct drm_display_mode *mode);
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