[bug report] drm/amd/display: Add MST atomic routines

[Dan Carpenter]

Hello Mikita Lipski,

The patch b4c578f08378: "drm/amd/display: Add MST atomic routines"
from Nov 6, 2019, leads to the following static checker warning:

	drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:4870 dm_encoder_helper_atomic_check()
	warn: unsigned 'dm_new_connector_state->vcpi_slots' is never less than zero.

drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c
  4851          if (!aconnector->port || !aconnector->dc_sink)
  4852                  return 0;
  4853  
  4854          mst_port = aconnector->port;
  4855          mst_mgr = &aconnector->mst_port->mst_mgr;
  4856  
  4857          if (!crtc_state->connectors_changed && !crtc_state->mode_changed)
  4858                  return 0;
  4859  
  4860          if (!state->duplicated) {
  4861                  color_depth = convert_color_depth_from_display_info(connector, conn_state);
  4862                  bpp = convert_dc_color_depth_into_bpc(color_depth) * 3;
  4863                  clock = adjusted_mode->clock;
  4864                  dm_new_connector_state->pbn = drm_dp_calc_pbn_mode(clock, bpp);
  4865          }
  4866          dm_new_connector_state->vcpi_slots = drm_dp_atomic_find_vcpi_slots(state,
  4867                                                                             mst_mgr,
  4868                                                                             mst_port,
  4869                                                                             dm_new_connector_state->pbn);
  4870          if (dm_new_connector_state->vcpi_slots < 0) {
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Impossible condition.

  4871                  DRM_DEBUG_ATOMIC("failed finding vcpi slots: %d\n", (int)dm_new_connector_state->vcpi_slots);
  4872                  return dm_new_connector_state->vcpi_slots;
  4873          }
  4874          return 0;
  4875  }

regards,
dan carpenter