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

[Daniel Vetter]

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.

> +		     "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 :-)

> +
>  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