drm/i915: provide more error output when mode sets fail

If a mode set fails we may get a message from drm_crtc_helper if we're lucky,
but it won't tell us anything about *why* we failed to set a mode.  So
add a few DRM_ERRORs for the cases that shouldn't happen so we can debug
things more easily.
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: NKeith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/intel_display.c

@@ -2096,7 +2096,7 @@ intel_pipe_set_base(struct drm_crtc *crtc, int x, int y,
 
 	/* no fb bound */
 	if (!crtc->fb) {
-		DRM_DEBUG_KMS("No FB bound\n");
+		DRM_ERROR("No FB bound\n");
 		return 0;
 	}
 
@@ -2105,6 +2105,7 @@ intel_pipe_set_base(struct drm_crtc *crtc, int x, int y,
 	case 1:
 		break;
 	default:
+		DRM_ERROR("no plane for crtc\n");
 		return -EINVAL;
 	}
 
@@ -2114,6 +2115,7 @@ intel_pipe_set_base(struct drm_crtc *crtc, int x, int y,
 					 NULL);
 	if (ret != 0) {
 		mutex_unlock(&dev->struct_mutex);
+		DRM_ERROR("pin & fence failed\n");
 		return ret;
 	}
 
@@ -2142,6 +2144,7 @@ intel_pipe_set_base(struct drm_crtc *crtc, int x, int y,
 	if (ret) {
 		i915_gem_object_unpin(to_intel_framebuffer(crtc->fb)->obj);
 		mutex_unlock(&dev->struct_mutex);
+		DRM_ERROR("failed to update base address\n");
 		return ret;
 	}