drm/fsl-dcu: disable planes before disabling CRTC

After disabling and reenabling the CRTC the DCU sometimes got stuck
displaying the whole screen with a solid color. Disabling and
reenabling the CRTC did not recover from the situation. This was
often reproducable by just restarting the X-Server.

The disabling sequence is not explicitly documented. But it turns
out that disabling the planes before disabling the CRTC seems to
prevent the above situation from happening.

Use the callback ->atomic_disable instead of ->disable which allows
to use the drm_atomic_helper_disable_planes_on_crtc() helper to
disable planes before disabling the controller.
Signed-off-by: Stefan Agner <stefan@agner.ch>

drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_crtc.c

@@ -44,11 +44,15 @@ static void fsl_dcu_drm_crtc_atomic_flush(struct drm_crtc *crtc,
 	}
 }
 
-static void fsl_dcu_drm_disable_crtc(struct drm_crtc *crtc)
+static void fsl_dcu_drm_crtc_atomic_disable(struct drm_crtc *crtc,
+					struct drm_crtc_state *old_crtc_state)
 {
 	struct drm_device *dev = crtc->dev;
 	struct fsl_dcu_drm_device *fsl_dev = dev->dev_private;
 
+	/* always disable planes on the CRTC */
+	drm_atomic_helper_disable_planes_on_crtc(old_crtc_state, true);
+
 	drm_crtc_vblank_off(crtc);
 
 	regmap_update_bits(fsl_dev->regmap, DCU_DCU_MODE,
@@ -127,8 +131,8 @@ static void fsl_dcu_drm_crtc_mode_set_nofb(struct drm_crtc *crtc)
 }
 
 static const struct drm_crtc_helper_funcs fsl_dcu_drm_crtc_helper_funcs = {
+	.atomic_disable = fsl_dcu_drm_crtc_atomic_disable,
 	.atomic_flush = fsl_dcu_drm_crtc_atomic_flush,
-	.disable = fsl_dcu_drm_disable_crtc,
 	.enable = fsl_dcu_drm_crtc_enable,
 	.mode_set_nofb = fsl_dcu_drm_crtc_mode_set_nofb,
 };