Re: [PATCH 01/20] drm/atomic: Fix remaining places where !funcs->best_encoder is valid

[Boris Brezillon <boris.brezillon@free-electrons.com>]

On Fri, 03 Jun 2016 00:05:46 +0300
Laurent Pinchart <laurent.pinchart@ideasonboard.com> wrote:

> Hi Boris,
> 
> Thank you for the patch.
> 
> On Thursday 02 Jun 2016 16:31:28 Boris Brezillon wrote:
> > Adapt drm_pick_crtcs() and update_connector_routing() to fallback to
> > drm_atomic_helper_best_encoder() if funcs->best_encoder() is NULL so
> > that DRM drivers can leave this hook unassigned if they know they want
> > to use drm_atomic_helper_best_encoder().  
> 
> Could you please update include/drm/drm_modeset_helper_vtables.h to document 
> this new behaviour ?

Sure.

> 
> The only drawback I see in this patch is the additional object lookup 
> performed by drm_atomic_helper_best_encoder() at runtime. I wonder if we could 
> somehow cache the information, as the assignment can't change when there's a 
> 1:1 correspondence between encoders and connectors.
> 
> > Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
> > ---
> >  drivers/gpu/drm/drm_atomic_helper.c |  4 +++-
> >  drivers/gpu/drm/drm_fb_helper.c     | 13 ++++++++++++-
> >  2 files changed, 15 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c
> > b/drivers/gpu/drm/drm_atomic_helper.c index f6a3350..849d029 100644
> > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > @@ -300,8 +300,10 @@ update_connector_routing(struct drm_atomic_state
> > *state, if (funcs->atomic_best_encoder)
> >  		new_encoder = funcs->atomic_best_encoder(connector,
> >  							 connector_state);
> > -	else
> > +	else if (funcs->best_encoder)
> >  		new_encoder = funcs->best_encoder(connector);
> > +	else
> > +		new_encoder = drm_atomic_helper_best_encoder(connector);
> > 
> >  	if (!new_encoder) {
> >  		DRM_DEBUG_ATOMIC("No suitable encoder found for [CONNECTOR:%d:%s]\n",
> > diff --git a/drivers/gpu/drm/drm_fb_helper.c
> > b/drivers/gpu/drm/drm_fb_helper.c index 7c2eb75..d44389a 100644
> > --- a/drivers/gpu/drm/drm_fb_helper.c
> > +++ b/drivers/gpu/drm/drm_fb_helper.c
> > @@ -2000,7 +2000,18 @@ static int drm_pick_crtcs(struct drm_fb_helper
> > *fb_helper, my_score++;
> > 
> >  	connector_funcs = connector->helper_private;
> > -	encoder = connector_funcs->best_encoder(connector);
> > +
> > +	/*
> > +	 * If the DRM device implements atomic hooks and ->best_encoder() is
> > +	 * NULL we fallback to the default drm_atomic_helper_best_encoder()
> > +	 * helper.
> > +	 */
> > +	if (fb_helper->dev->mode_config.funcs->atomic_commit &&
> > +	    !connector_funcs->best_encoder)
> > +		encoder = drm_atomic_helper_best_encoder(connector);
> > +	else
> > +		encoder = connector_funcs->best_encoder(connector);
> > +
> >  	if (!encoder)
> >  		goto out;  
> 



-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com