drm/atomic-helper: Add atomic_disable CRTC helper callback

Some display controllers need plane(s) to be disabled together with
the relevant CRTC, e.g., the IPUv3 display controller for imx-drm.
This patch adds atomic_disable CRTC helper callback so that
old_crtc_state(as a parameter of the callback) could be used
to get the active plane(s) of the old CRTC state for disable operation.

Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Peter Senna Tschudin <peter.senna@gmail.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Liu Ying <gnuiyl@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1472196644-30563-2-git-send-email-gnuiyl@gmail.com

drivers/gpu/drm/drm_atomic_helper.c

@@ -749,6 +749,8 @@ disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
 		/* Right function depends upon target state. */
 		if (crtc->state->enable && funcs->prepare)
 			funcs->prepare(crtc);
+		else if (funcs->atomic_disable)
+			funcs->atomic_disable(crtc, old_crtc_state);
 		else if (funcs->disable)
 			funcs->disable(crtc);
 		else

include/drm/drm_modeset_helper_vtables.h

@@ -266,6 +266,8 @@ struct drm_crtc_helper_funcs {
 	 * disable anything at the CRTC level. To ensure that runtime PM
 	 * handling (using either DPMS or the new "ACTIVE" property) works
 	 * @disable must be the inverse of @enable for atomic drivers.
+	 * Atomic drivers should consider to use @atomic_disable instead of
+	 * this one.
 	 *
 	 * NOTE:
 	 *
@@ -391,6 +393,28 @@ struct drm_crtc_helper_funcs {
 	 */
 	void (*atomic_flush)(struct drm_crtc *crtc,
 			     struct drm_crtc_state *old_crtc_state);
+
+	/**
+	 * @atomic_disable:
+	 *
+	 * This callback should be used to disable the CRTC. With the atomic
+	 * drivers it is called after all encoders connected to this CRTC have
+	 * been shut off already using their own ->disable hook. If that
+	 * sequence is too simple drivers can just add their own hooks and call
+	 * it from this CRTC callback here by looping over all encoders
+	 * connected to it using for_each_encoder_on_crtc().
+	 *
+	 * This hook is used only by atomic helpers. Atomic drivers don't
+	 * need to implement it if there's no need to disable anything at the
+	 * CRTC level.
+	 *
+	 * Comparing to @disable, this one provides the additional input
+	 * parameter @old_crtc_state which could be used to access the old
+	 * state. Atomic drivers should consider to use this one instead
+	 * of @disable.
+	 */
+	void (*atomic_disable)(struct drm_crtc *crtc,
+			       struct drm_crtc_state *old_crtc_state);
 };
 
 /**