Re: [PATCH v3 7/7] drm: Allow drivers to leave encoder->possible_crtcs==0

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Feb 11, 2020 at 06:05:45PM +0100, Daniel Vetter wrote:
> On Tue, Feb 11, 2020 at 06:22:08PM +0200, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > Let's simplify life of driver by allowing them to leave
> > encoder->possible_crtcs unset if they have no restrictions
> > in crtc<->encoder linkage. We'll just populate possible_crtcs
> > with the full crtc mask when registering the encoder so that
> > userspace doesn't have to deal with drivers not populating
> > this correctly.
> > 
> > Cc: Thomas Zimmermann <tzimmermann@suse.de>
> > Cc: Daniel Vetter <daniel@ffwll.ch>
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> > We might not actually need/want this, but included it here for
> > future reference if that assumption turns out to be wrong.
> 
> I think this one is most definitely needed. _Lots_ of drivers get this
> toally wrong and just leave the value blank. It's encoded as official
> fallback in most userspace compositors.

OK. It's been a while since I dug around so can't really remmber how
this was being handled. I'll reorder before pushing.

> 
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
> > ---
> >  drivers/gpu/drm/drm_mode_config.c | 15 ++++++++++++++-
> >  include/drm/drm_encoder.h         |  4 ++++
> >  2 files changed, 18 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> > index 4c1b350ddb95..ce18c3dd0bde 100644
> > --- a/drivers/gpu/drm/drm_mode_config.c
> > +++ b/drivers/gpu/drm/drm_mode_config.c
> > @@ -592,6 +592,17 @@ static u32 full_crtc_mask(struct drm_device *dev)
> >  	return crtc_mask;
> >  }
> >  
> > +/*
> > + * Make life easy for drivers by allowing them to leave
> > + * possible_crtcs unset if there are not crtc<->encoder
> > + * restrictions.
> > + */
> > +static void fixup_encoder_possible_crtcs(struct drm_encoder *encoder)
> > +{
> > +	if (encoder->possible_crtcs == 0)
> > +		encoder->possible_crtcs = full_crtc_mask(encoder->dev);
> > +}
> > +
> >  static void validate_encoder_possible_crtcs(struct drm_encoder *encoder)
> >  {
> >  	u32 crtc_mask = full_crtc_mask(encoder->dev);
> > @@ -608,8 +619,10 @@ void drm_mode_config_validate(struct drm_device *dev)
> >  {
> >  	struct drm_encoder *encoder;
> >  
> > -	drm_for_each_encoder(encoder, dev)
> > +	drm_for_each_encoder(encoder, dev) {
> >  		fixup_encoder_possible_clones(encoder);
> > +		fixup_encoder_possible_crtcs(encoder);
> > +	}
> >  
> >  	drm_for_each_encoder(encoder, dev) {
> >  		validate_encoder_possible_clones(encoder);
> > diff --git a/include/drm/drm_encoder.h b/include/drm/drm_encoder.h
> > index b236269f41ac..bd033c5618bf 100644
> > --- a/include/drm/drm_encoder.h
> > +++ b/include/drm/drm_encoder.h
> > @@ -142,6 +142,10 @@ struct drm_encoder {
> >  	 * the bits for all &drm_crtc objects this encoder can be connected to
> >  	 * before calling drm_dev_register().
> >  	 *
> > +	 * As an exception to the above rule if any crtc can be connected to
> > +	 * the encoder the driver can leave @possible_crtcs set to 0. The core
> > +	 * will automagically fix this up by setting the bit for every crtc.
> > +	 *
> >  	 * You will get a WARN if you get this wrong in the driver.
> >  	 *
> >  	 * Note that since CRTC objects can't be hotplugged the assigned indices
> > -- 
> > 2.24.1
> > 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

-- 
Ville Syrjälä
Intel
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