[bug report] drm/amd/display: Only register backlight device if embedded panel connected

[Dan Carpenter]

Hello Harry Wentland,

The patch 89fc8d4e95e7: "drm/amd/display: Only register backlight
device if embedded panel connected" from Mar 12, 2018, leads to the
following static checker warning:

	drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:1785 amdgpu_dm_initialize_drm_device()
	warn: 'i' is out of bounds '31' vs '11'

drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c
  1756          /* loops over all connectors on the board */
  1757          for (i = 0; i < link_cnt; i++) {
                                ^^^^^^^^

I believe the link_cnt is at most 12?  Smatch has trouble figuring it
out.

  1758                  struct dc_link *link = NULL;
  1759  
  1760                  if (i > AMDGPU_DM_MAX_DISPLAY_INDEX) {
                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^
This is 32 so Smatch says that i can go up to 31.

  1761                          DRM_ERROR(
  1762                                  "KMS: Cannot support more than %d display indexes\n",
  1763                                          AMDGPU_DM_MAX_DISPLAY_INDEX);
  1764                          continue;
  1765                  }
  1766  
  1767                  aconnector = kzalloc(sizeof(*aconnector), GFP_KERNEL);
  1768                  if (!aconnector)
  1769                          goto fail;
  1770  
  1771                  aencoder = kzalloc(sizeof(*aencoder), GFP_KERNEL);
  1772                  if (!aencoder)
  1773                          goto fail;
  1774  
  1775                  if (amdgpu_dm_encoder_init(dm->ddev, aencoder, i)) {
  1776                          DRM_ERROR("KMS: Failed to initialize encoder\n");
  1777                          goto fail;
  1778                  }
  1779  
  1780                  if (amdgpu_dm_connector_init(dm, aconnector, i, aencoder)) {
  1781                          DRM_ERROR("KMS: Failed to initialize connector\n");
  1782                          goto fail;
  1783                  }
  1784  
  1785                  link = dc_get_link_at_index(dm->dc, i);
                                                            ^
Which would be a problem here.  Can we just delete the misleading
AMDGPU_DM_MAX_DISPLAY_INDEX comparison?

  1786  
  1787                  if (!dc_link_detect_sink(link, &new_connection_type))
  1788                          DRM_ERROR("KMS: Failed to detect connector\n");
  1789  
  1790                  if (aconnector->base.force && new_connection_type == dc_connection_none) {
  1791                          emulated_link_detect(link);
  1792                          amdgpu_dm_update_connector_after_detect(aconnector);
  1793  
  1794                  } else if (dc_link_detect(link, DETECT_REASON_BOOT)) {
  1795                          amdgpu_dm_update_connector_after_detect(aconnector);
  1796                          register_backlight_device(dm, link);
  1797                  }
  1798  
  1799  
  1800          }

regards,
dan carpenter