[bug report] drm/sun4i: backend: Check for the number of alpha planes

[Dan Carpenter]

Hello Maxime Ripard,

The patch 65f7fa3a3fcb: "drm/sun4i: backend: Check for the number of
alpha planes" from Jun 26, 2017, leads to the following static
checker warning:

	drivers/gpu/drm/sun4i/sun4i_backend.c:486 sun4i_backend_atomic_check()
	error: 'plane_state' dereferencing possible ERR_PTR()

drivers/gpu/drm/sun4i/sun4i_backend.c
   462  static int sun4i_backend_atomic_check(struct sunxi_engine *engine,
   463                                        struct drm_crtc_state *crtc_state)
   464  {
   465          struct drm_plane_state *plane_states[SUN4I_BACKEND_NUM_LAYERS] = { 0 };
   466          struct drm_atomic_state *state = crtc_state->state;
   467          struct drm_device *drm = state->dev;
   468          struct drm_plane *plane;
   469          unsigned int num_planes = 0;
   470          unsigned int num_alpha_planes = 0;
   471          unsigned int num_frontend_planes = 0;
   472          unsigned int num_yuv_planes = 0;
   473          unsigned int current_pipe = 0;
   474          unsigned int i;
   475  
   476          DRM_DEBUG_DRIVER("Starting checking our planes\n");
   477  
   478          if (!crtc_state->planes_changed)
   479                  return 0;
   480  
   481          drm_for_each_plane_mask(plane, drm, crtc_state->plane_mask) {
   482                  struct drm_plane_state *plane_state =
   483                          drm_atomic_get_plane_state(state, plane);
                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Not checked for failure.

   484                  struct sun4i_layer_state *layer_state =
   485                          state_to_sun4i_layer_state(plane_state);
   486                  struct drm_framebuffer *fb = plane_state->fb;
   487                  struct drm_format_name_buf format_name;
   488  
   489                  if (sun4i_backend_plane_uses_frontend(plane_state)) {
   490                          DRM_DEBUG_DRIVER("Using the frontend for plane %d\n",
   491                                           plane->index);
   492  
   493                          layer_state->uses_frontend = true;
   494                          num_frontend_planes++;
   495                  } else {
   496                          layer_state->uses_frontend = false;
   497                  }

regards,
dan carpenter