Re: [PATCH] drm/i915: Ensure plane->state->fb stays in sync with plane->fb

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Feb 03, 2015 at 01:10:04PM -0800, Matt Roper wrote:
> plane->state->fb and plane->fb should always reference the same FB so
> that atomic and legacy codepaths have the same view of display state.
> In commit
> 
>         commit db068420560511de80ac59222644f2bdf278c3d5
>         Author: Matt Roper <matthew.d.roper@intel.com>
>         Date:   Fri Jan 30 16:22:36 2015 -0800
> 
>             drm/i915: Keep plane->state updated on pageflip
> 
> we already fixed one case where these two pointers could get out of
> sync.  However it turns out there are a few other places (mainly dealing
> with initial FB setup at boot) that directly set plane->fb and neglect
> to update plane->state->fb.  If we never do a successful update through
> the atomic pipeline, the RmFB cleanup code will look at the
> plane->state->fb pointer, which has never actually been set to a
> legitimate value, and try to clean it up, leading to BUG's.
> 
> Add a quick helper function to synchronize plane->state->fb with
> plane->fb (and update reference counts accordingly) and call it
> everywhere the driver tries to manually set plane->fb outside of the
> atomic pipeline.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88909
> Signed-off-by: Matt Roper <matthew.d.roper@intel.com>

Unrelated thing I've spotted while reviewing this: We still update
plane->fb in our plane commit hooks, but helpers should take care of that.
Do we still have these because our code still looks at plane->fb instead
of plane->state->fb or is there some deeper reason?

I think a large-scale s/plane->fb/plane->state->fb/ and then removing
those and relying upon the fixup code in the helpers/core would be good.
Unfortunately we can't cocci this since we need to keep a few ...

Anyway, patch lgtm and is merged.

Thanks, Daniel
> ---
>  drivers/gpu/drm/i915/intel_display.c | 29 ++++++++++++++++++++++-------
>  1 file changed, 22 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 213b870..e5c0579 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -2410,6 +2410,20 @@ out_unref_obj:
>  	return false;
>  }
>  
> +/* Update plane->state->fb to match plane->fb after driver-internal updates */
> +static void
> +update_state_fb(struct drm_plane *plane)
> +{
> +	if (plane->fb == plane->state->fb)
> +		return;
> +
> +	if (plane->state->fb)
> +		drm_framebuffer_unreference(plane->state->fb);
> +	plane->state->fb = plane->fb;
> +	if (plane->state->fb)
> +		drm_framebuffer_reference(plane->state->fb);
> +}
> +
>  static void
>  intel_find_plane_obj(struct intel_crtc *intel_crtc,
>  		     struct intel_initial_plane_config *plane_config)
> @@ -2456,6 +2470,8 @@ intel_find_plane_obj(struct intel_crtc *intel_crtc,
>  			break;
>  		}
>  	}
> +
> +	update_state_fb(intel_crtc->base.primary);
>  }
>  
>  static void i9xx_update_primary_plane(struct drm_crtc *crtc,
> @@ -6635,6 +6651,7 @@ i9xx_get_initial_plane_config(struct intel_crtc *crtc,
>  		      plane_config->size);
>  
>  	crtc->base.primary->fb = fb;
> +	update_state_fb(crtc->base.primary);
>  }
>  
>  static void chv_crtc_clock_get(struct intel_crtc *crtc,
> @@ -7672,6 +7689,7 @@ skylake_get_initial_plane_config(struct intel_crtc *crtc,
>  		      plane_config->size);
>  
>  	crtc->base.primary->fb = fb;
> +	update_state_fb(crtc->base.primary);
>  	return;
>  
>  error:
> @@ -7763,6 +7781,7 @@ ironlake_get_initial_plane_config(struct intel_crtc *crtc,
>  		      plane_config->size);
>  
>  	crtc->base.primary->fb = fb;
> +	update_state_fb(crtc->base.primary);
>  }
>  
>  static bool ironlake_get_pipe_config(struct intel_crtc *crtc,
> @@ -9800,13 +9819,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
>  	drm_gem_object_reference(&obj->base);
>  
>  	crtc->primary->fb = fb;
> -
> -	/* Keep state structure in sync */
> -	if (crtc->primary->state->fb)
> -		drm_framebuffer_unreference(crtc->primary->state->fb);
> -	crtc->primary->state->fb = fb;
> -	if (crtc->primary->state->fb)
> -		drm_framebuffer_reference(crtc->primary->state->fb);
> +	update_state_fb(crtc->primary);
>  
>  	work->pending_flip_obj = obj;
>  
> @@ -9875,6 +9888,7 @@ cleanup_unpin:
>  cleanup_pending:
>  	atomic_dec(&intel_crtc->unpin_work_count);
>  	crtc->primary->fb = old_fb;
> +	update_state_fb(crtc->primary);
>  	drm_framebuffer_unreference(work->old_fb);
>  	drm_gem_object_unreference(&obj->base);
>  	mutex_unlock(&dev->struct_mutex);
> @@ -13709,6 +13723,7 @@ void intel_modeset_gem_init(struct drm_device *dev)
>  				  to_intel_crtc(c)->pipe);
>  			drm_framebuffer_unreference(c->primary->fb);
>  			c->primary->fb = NULL;
> +			update_state_fb(c->primary);
>  		}
>  	}
>  	mutex_unlock(&dev->struct_mutex);
> -- 
> 1.8.5.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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