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

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

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@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@suse.de>
> > Cc: Daniel Vetter <daniel@ffwll.ch>
> > Signed-off-by: Ville Syrjälä <ville.syrjala@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.

> 
> > +
> >  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@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
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