[PATCH v3 5/7] drm: Validate encoder->possible_clones

[Daniel Vetter]

On Tue, Feb 11, 2020 at 07:13:31PM +0200, Ville Syrjälä wrote:
> On Tue, Feb 11, 2020 at 06:02:33PM +0100, Daniel Vetter wrote:
> > On Tue, Feb 11, 2020 at 06:22:06PM +0200, Ville Syrjala wrote:
> > > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > 
> > > Many drivers are populating encoder->possible_clones wrong. Let's
> > > persuade them to get it right by adding some loud WARNs.
> > > 
> > > We'll cross check the bits between any two encoders. So either
> > > both encoders can clone with the other, or neither can.
> > > 
> > > We'll also complain about effectively empty possible_clones, and
> > > possible_clones containing bits for encoders that don't exist.
> > > 
> > > v2: encoder->possible_clones now includes the encoder itelf
> > > v3: Move to drm_mode_config_validate() (Daniel)
> > >     Document that you get a WARN when this is wrong (Daniel)
> > >     Extract full_encoder_mask()
> > > 
> > > Acked-by: Thomas Zimmermann <tzimmermann at suse.de>
> > > Cc: Daniel Vetter <daniel at ffwll.ch>
> > > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > I wonder whether we should start to have some unit tests for stuff like
> > this, like set up broken driver, make sure we have a WARN in dmesg. But
> > ideally we'd do that with the mocking stuff Kunit hopefully has soon.
> > 
> > </idle musings>
> > 
> > 
> > > ---
> > >  drivers/gpu/drm/drm_mode_config.c | 40 +++++++++++++++++++++++++++++++
> > >  include/drm/drm_encoder.h         |  2 ++
> > >  2 files changed, 42 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> > > index 75e357c7e84d..afc91447293a 100644
> > > --- a/drivers/gpu/drm/drm_mode_config.c
> > > +++ b/drivers/gpu/drm/drm_mode_config.c
> > > @@ -533,6 +533,17 @@ void drm_mode_config_cleanup(struct drm_device *dev)
> > >  }
> > >  EXPORT_SYMBOL(drm_mode_config_cleanup);
> > >  
> > > +static u32 full_encoder_mask(struct drm_device *dev)
> > > +{
> > > +	struct drm_encoder *encoder;
> > > +	u32 encoder_mask = 0;
> > > +
> > > +	drm_for_each_encoder(encoder, dev)
> > > +		encoder_mask |= drm_encoder_mask(encoder);
> > > +
> > > +	return encoder_mask;
> > > +}
> > > +
> > >  /*
> > >   * For some reason we want the encoder itself included in
> > >   * possible_clones. Make life easy for drivers by allowing them
> > > @@ -544,10 +555,39 @@ static void fixup_encoder_possible_clones(struct drm_encoder *encoder)
> > >  		encoder->possible_clones = drm_encoder_mask(encoder);
> > >  }
> > >  
> > > +static void validate_encoder_possible_clones(struct drm_encoder *encoder)
> > > +{
> > > +	struct drm_device *dev = encoder->dev;
> > > +	u32 encoder_mask = full_encoder_mask(dev);
> > > +	struct drm_encoder *other;
> > > +
> > > +	drm_for_each_encoder(other, dev) {
> > > +		WARN(!(encoder->possible_clones & drm_encoder_mask(other)) !=
> > > +		     !(other->possible_clones & drm_encoder_mask(encoder)),
> > 
> > Bikeshed: !! as canonical "make this a bool value" might be slightly
> > clearer, but whatever.
> 
> Can repaint.
> 
> > 
> > > +		     "possible_clones mismatch: "
> > > +		     "[ENCODER:%d:%s] mask=0x%x possible_clones=0x%x vs. "
> > > +		     "[ENCODER:%d:%s] mask=0x%x possible_clones=0x%x\n",
> > > +		     encoder->base.id, encoder->name,
> > > +		     drm_encoder_mask(encoder), encoder->possible_clones,
> > > +		     other->base.id, other->name,
> > > +		     drm_encoder_mask(other), other->possible_clones);
> > > +	}
> > > +
> > > +	WARN((encoder->possible_clones & drm_encoder_mask(encoder)) == 0 ||
> > > +	     (encoder->possible_clones & ~encoder_mask) != 0,
> > > +	     "Bogus possible_clones: "
> > > +	     "[ENCODER:%d:%s] possible_clones=0x%x (full encoder mask=0x%x)\n",
> > > +	     encoder->base.id, encoder->name,
> > > +	     encoder->possible_clones, encoder_mask);
> > > +}
> > 
> > Since it's next to each another double-checking that the fixup did add the
> > self-clone is probably too much :-)
> 
> I changed the fixup to be just
> if (possible_clones == 0)
> 	possible_clones = drm_encoder_mask();
> 
> So if the driver tries to set it up but fails and forgets the
> encoder itself this WARN will still trip.

Duh, I was just blind, everything is looking good.
-Daniel

> 
> > 
> > > +
> > >  void drm_mode_config_validate(struct drm_device *dev)
> > >  {
> > >  	struct drm_encoder *encoder;
> > >  
> > >  	drm_for_each_encoder(encoder, dev)
> > >  		fixup_encoder_possible_clones(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 22d6cdf729f1..3741963b9587 100644
> > > --- a/include/drm/drm_encoder.h
> > > +++ b/include/drm/drm_encoder.h
> > > @@ -163,6 +163,8 @@ struct drm_encoder {
> > >  	 * any cloning it can leave @possible_clones set to 0. The core will
> > >  	 * automagically fix this up by setting the bit for the encoder itself.
> > >  	 *
> > > +	 * You will get a WARN if you get this wrong in the driver.
> > 
> > Nice.
> > 
> > Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> > 
> > > +	 *
> > >  	 * Note that since encoder objects can't be hotplugged the assigned indices
> > >  	 * are stable and hence known before registering all objects.
> > >  	 */
> > > -- 
> > > 2.24.1
> > > 
> > 
> > -- 
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch
> 
> -- 
> Ville Syrjälä
> Intel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch