[PATCH 01/10] drm/atomic: Add __drm_atomic_helper_plane_reset

[Boris Brezillon]

On Tue, 24 Jul 2018 09:14:02 +0100
Alexandru-Cosmin Gheorghe <Alexandru-Cosmin.Gheorghe at arm.com> wrote:

> On Tue, Jul 24, 2018 at 09:48:53AM +0200, Philipp Zabel wrote:
> > Hi Alexandru,
> > 
> > On Fri, 2018-07-20 at 22:15 +0100, Alexandru Gheorghe wrote:  
> > > There are a lot of drivers that subclass drm_plane_state, all of them
> > > duplicate the code that links toghether the plane with plane_state.
> > > 
> > > On top of that, drivers that enable core properties also have to
> > > duplicate the code for initializing the properties to their default
> > > values, which in all cases are the same as the defaults from core.
> > > 
> > > Signed-off-by: Alexandru Gheorghe <alexandru-cosmin.gheorghe at arm.com>
> > > ---
> > >  drivers/gpu/drm/drm_atomic_helper.c | 32 +++++++++++++++++++++--------
> > >  include/drm/drm_atomic_helper.h     |  2 ++
> > >  2 files changed, 25 insertions(+), 9 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > > index 8008a7de2e10..e1c6f101652e 100644
> > > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > > @@ -3507,6 +3507,28 @@ void drm_atomic_helper_crtc_destroy_state(struct drm_crtc *crtc,
> > >  }
> > >  EXPORT_SYMBOL(drm_atomic_helper_crtc_destroy_state);
> > >  
> > > +/**
> > > + * __drm_atomic_helper_plane_reset - resets planes state to default values
> > > + * @plane: plane object
> > > + * @new_state: atomic plane state
> > > + *
> > > + * Initializes plane state to default. This is useful for drivers that subclass
> > > + * the plane state.
> > > + */
> > > +void __drm_atomic_helper_plane_reset(struct drm_plane *plane,
> > > +				     struct drm_plane_state *state)
> > > +{
> > > +	if (state) {
> > > +		state->plane = plane;
> > > +		state->rotation = DRM_MODE_ROTATE_0;
> > > +		/* Reset the alpha value to fully opaque if it matters */
> > > +		if (plane->alpha_property)
> > > +			state->alpha = plane->alpha_property->values[1];
> > > +	}  
> > 
> > Is this function supposed to be callable with state == NULL ?
> >   
> > > +	plane->state = state;  
> > 
> > If so, the comment could mention that this sets plane->state to NULL if
> > state == NULL, and a few of the call sites could be simplified.
> > 
> > If not, I would remove the conditional if (state) {} part and also
> > mention this in the comment.  
> 
> Yes, It's intended to be callable with null.

May I ask why? I'd assume drivers that call this function to pass a
non-NULL plane state. What's the use case for passing a NULL state here?