[Intel-gfx] [bug report] drm/i915: Fix enabled_planes bitmask

[Dan Carpenter]

Hello Ville Syrjälä,

This is a semi-automatic email about new static checker warnings.

The patch 97bc7ffa1b1e: "drm/i915: Fix enabled_planes bitmask" from
Mar 5, 2021, leads to the following Smatch complaint:

    drivers/gpu/drm/i915/display/intel_atomic_plane.c:332 intel_plane_atomic_check_with_state()
    error: we previously assumed 'fb' could be null (see line 324)

drivers/gpu/drm/i915/display/intel_atomic_plane.c
   323	
   324		if (fb)
                    ^^
The patch adds a check for NULL

   325			new_crtc_state->enabled_planes |= BIT(plane->id);
   326	
   327		/* FIXME pre-g4x don't work like this */
   328		if (new_plane_state->uapi.visible)
   329			new_crtc_state->active_planes |= BIT(plane->id);
   330	
   331		if (new_plane_state->uapi.visible &&
   332		    intel_format_info_is_yuv_semiplanar(fb->format, fb->modifier))
                                                        ^^^^^^^^^^^^^^^^^^^^^^^^
Unchecked deref

   333			new_crtc_state->nv12_planes |= BIT(plane->id);
   334	
   335          if (new_plane_state->uapi.visible &&
   336              fb->format->format == DRM_FORMAT_C8)
                    ^^^^^^^^^^
Same.  These are potentially false positives.  I don't know if
"uapi.visible" can be true when ctrc is non-NULL and fb is NULL for
example?  (The point is I read the commit message, but I know pants all
about DRM.  :P)

   337                  new_crtc_state->c8_planes |= BIT(plane->id);
   338  
   339          if (new_plane_state->uapi.visible || old_plane_state->uapi.visible)
   340                  new_crtc_state->update_planes |= BIT(plane->id);
   341  
   342          new_crtc_state->data_rate[plane->id] =
   343                  intel_plane_data_rate(new_crtc_state, new_plane_state);
   344  
   345          return intel_plane_atomic_calc_changes(old_crtc_state, new_crtc_state,
   346                                                 old_plane_state, new_plane_state);
   347  }

regards,
dan carpenter