drm/simple-helpers: Always add planes to the state update

Our update function is hooked to the single plane, which might not get
called for crtc-only updates. Which is surprising, so fix this by
always adding the plane.

While at it document how&when the event should be sent out better in
the kerneldoc.

Cc: Noralf Trønnes <noralf@tronnes.org>
Cc: andrea.merello@gmail.com
Tested-and-Reported-by: andrea.merello@gmail.com
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1471933540-31131-1-git-send-email-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_simple_kms_helper.c

@@ -34,6 +34,12 @@ static const struct drm_encoder_funcs drm_simple_kms_encoder_funcs = {
 	.destroy = drm_encoder_cleanup,
 };
 
+static int drm_simple_kms_crtc_check(struct drm_crtc *crtc,
+				     struct drm_crtc_state *state)
+{
+	return drm_atomic_add_affected_planes(state->state, crtc);
+}
+
 static void drm_simple_kms_crtc_enable(struct drm_crtc *crtc)
 {
 	struct drm_simple_display_pipe *pipe;
@@ -57,6 +63,7 @@ static void drm_simple_kms_crtc_disable(struct drm_crtc *crtc)
 }
 
 static const struct drm_crtc_helper_funcs drm_simple_kms_crtc_helper_funcs = {
+	.atomic_check = drm_simple_kms_crtc_check,
 	.disable = drm_simple_kms_crtc_disable,
 	.enable = drm_simple_kms_crtc_enable,
 };

include/drm/drm_simple_kms_helper.h

@@ -60,6 +60,12 @@ struct drm_simple_display_pipe_funcs {
 	 *
 	 * This function is called when the underlying plane state is updated.
 	 * This hook is optional.
+	 *
+	 * This is the function drivers should submit the
+	 * &drm_pending_vblank_event from. Using either
+	 * drm_crtc_arm_vblank_event(), when the driver supports vblank
+	 * interrupt handling, or drm_crtc_send_vblank_event() directly in case
+	 * the hardware lacks vblank support entirely.
 	 */
 	void (*update)(struct drm_simple_display_pipe *pipe,
 		       struct drm_plane_state *plane_state);