Hello Simon Ser,

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

The patch 03a663673063: "drm/amd/display: use FB pitch to fill 
dc_cursor_attributes" from Dec 2, 2020, leads to the following Smatch 
complaint:

    drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:7438 
handle_cursor_update()
    error: we previously assumed 'afb' could be null (see line 7397)

drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c
  7389  static void handle_cursor_update(struct drm_plane *plane,
  7390                                   struct drm_plane_state 
*old_plane_state)
  7391  {
  7392          struct amdgpu_device *adev = drm_to_adev(plane->dev);
  7393          struct amdgpu_framebuffer *afb = 
to_amdgpu_framebuffer(plane->state->fb);
                                           
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
If "plane->state->fb" is NULL then "afb" is NULL.


  7394          struct drm_crtc *crtc = afb ? plane->state->crtc : 
old_plane_state->crtc;
                                        ^^^
Checked for NULL.

  7395          struct dm_crtc_state *crtc_state = crtc ? 
to_dm_crtc_state(crtc->state) : NULL;
  7396          struct amdgpu_crtc *amdgpu_crtc = to_amdgpu_crtc(crtc);
  7397          uint64_t address = afb ? afb->address : 0;
  7398          struct dc_cursor_position position;
  7399          struct dc_cursor_attributes attributes;
  7400          int ret;
  7401  
  7402          if (!plane->state->fb && !old_plane_state->fb)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
These aren't allow to be both NULL

  7403                  return;
  7404  
  7405          DRM_DEBUG_DRIVER("%s: crtc_id=%d with size %d to %d\n",
  7406                           __func__,
  7407                           amdgpu_crtc->crtc_id,
  7408                           plane->state->crtc_w,
  7409                           plane->state->crtc_h);
  7410  
  7411          ret = get_cursor_position(plane, crtc, &position);
  7412          if (ret)
  7413                  return;
  7414  
  7415          if (!position.enable) {
  7416                  /* turn off cursor */
  7417                  if (crtc_state && crtc_state->stream) {
  7418                          mutex_lock(&adev->dm.dc_lock);
  7419                          
dc_stream_set_cursor_position(crtc_state->stream,
  7420                                                        &position);
  7421                          mutex_unlock(&adev->dm.dc_lock);
  7422                  }
  7423                  return;
  7424          }
  7425  
  7426          amdgpu_crtc->cursor_width = plane->state->crtc_w;
  7427          amdgpu_crtc->cursor_height = plane->state->crtc_h;
  7428  
  7429          memset(&attributes, 0, sizeof(attributes));
  7430          attributes.address.high_part = upper_32_bits(address);
  7431          attributes.address.low_part  = lower_32_bits(address);
  7432          attributes.width             = plane->state->crtc_w;
  7433          attributes.height            = plane->state->crtc_h;
  7434          attributes.color_format      = 
CURSOR_MODE_COLOR_PRE_MULTIPLIED_ALPHA;
  7435          attributes.rotation_angle    = 0;
  7436          attributes.attribute_flags.value = 0;
  7437  
  7438          attributes.pitch = afb->base.pitches[0] / 
afb->base.format->cpp[0];
                                   ^^^^^                  ^^^^^
The patch adds some new unchecked dereferences.

  7439  
  7440          if (crtc_state->stream) {

regards,
dan carpenter
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