drm/atomic-helper: Add atomic_enable plane-helper callback

Add atomic_enable to struct drm_plane_helper_funcs. It enables a
plane independently from updating the plane's content. As such, it is
the inverse of the atomic_disable plane helper. Useful for hardware
where plane enable state is independent from plane content.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230209154107.30680-2-tzimmermann@suse.de

drivers/gpu/drm/drm_atomic_helper.c

@@ -2702,6 +2702,11 @@ void drm_atomic_helper_commit_planes(struct drm_device *dev,
 			funcs->atomic_disable(plane, old_state);
 		} else if (new_plane_state->crtc || disabling) {
 			funcs->atomic_update(plane, old_state);
+
+			if (!disabling && funcs->atomic_enable) {
+				if (drm_atomic_plane_enabling(old_plane_state, new_plane_state))
+					funcs->atomic_enable(plane, old_state);
+			}
 		}
 	}
 
@@ -2762,6 +2767,7 @@ drm_atomic_helper_commit_planes_on_crtc(struct drm_crtc_state *old_crtc_state)
 		struct drm_plane_state *new_plane_state =
 			drm_atomic_get_new_plane_state(old_state, plane);
 		const struct drm_plane_helper_funcs *plane_funcs;
+		bool disabling;
 
 		plane_funcs = plane->helper_private;
 
@@ -2771,12 +2777,18 @@ drm_atomic_helper_commit_planes_on_crtc(struct drm_crtc_state *old_crtc_state)
 		WARN_ON(new_plane_state->crtc &&
 			new_plane_state->crtc != crtc);
 
-		if (drm_atomic_plane_disabling(old_plane_state, new_plane_state) &&
-		    plane_funcs->atomic_disable)
+		disabling = drm_atomic_plane_disabling(old_plane_state, new_plane_state);
+
+		if (disabling && plane_funcs->atomic_disable) {
 			plane_funcs->atomic_disable(plane, old_state);
-		else if (new_plane_state->crtc ||
-			 drm_atomic_plane_disabling(old_plane_state, new_plane_state))
+		} else if (new_plane_state->crtc || disabling) {
 			plane_funcs->atomic_update(plane, old_state);
+
+			if (!disabling && plane_funcs->atomic_enable) {
+				if (drm_atomic_plane_enabling(old_plane_state, new_plane_state))
+					plane_funcs->atomic_enable(plane, old_state);
+			}
+		}
 	}
 
 	if (crtc_funcs && crtc_funcs->atomic_flush)

include/drm/drm_atomic_helper.h

@@ -209,6 +209,32 @@ int drm_atomic_helper_page_flip_target(
 			      __drm_atomic_get_current_plane_state((crtc_state)->state, \
 								   plane)))
 
+/**
+ * drm_atomic_plane_enabling - check whether a plane is being enabled
+ * @old_plane_state: old atomic plane state
+ * @new_plane_state: new atomic plane state
+ *
+ * Checks the atomic state of a plane to determine whether it's being enabled
+ * or not. This also WARNs if it detects an invalid state (both CRTC and FB
+ * need to either both be NULL or both be non-NULL).
+ *
+ * RETURNS:
+ * True if the plane is being enabled, false otherwise.
+ */
+static inline bool drm_atomic_plane_enabling(struct drm_plane_state *old_plane_state,
+					     struct drm_plane_state *new_plane_state)
+{
+	/*
+	 * When enabling a plane, CRTC and FB should always be set together.
+	 * Anything else should be considered a bug in the atomic core, so we
+	 * gently warn about it.
+	 */
+	WARN_ON((!new_plane_state->crtc && new_plane_state->fb) ||
+		(new_plane_state->crtc && !new_plane_state->fb));
+
+	return !old_plane_state->crtc && new_plane_state->crtc;
+}
+
 /**
  * drm_atomic_plane_disabling - check whether a plane is being disabled
  * @old_plane_state: old atomic plane state

include/drm/drm_modeset_helper_vtables.h

@@ -1331,6 +1331,32 @@ struct drm_plane_helper_funcs {
 	 */
 	void (*atomic_update)(struct drm_plane *plane,
 			      struct drm_atomic_state *state);
+
+	/**
+	 * @atomic_enable:
+	 *
+	 * Drivers should use this function to unconditionally enable a plane.
+	 * This hook is called in-between the &drm_crtc_helper_funcs.atomic_begin
+	 * and drm_crtc_helper_funcs.atomic_flush callbacks. It is called after
+	 * @atomic_update, which will be called for all enabled planes. Drivers
+	 * that use @atomic_enable should set up a plane in @atomic_update and
+	 * afterwards enable the plane in @atomic_enable. If a plane needs to be
+	 * enabled before installing the scanout buffer, drivers can still do
+	 * so in @atomic_update.
+	 *
+	 * Note that the power state of the display pipe when this function is
+	 * called depends upon the exact helpers and calling sequence the driver
+	 * has picked. See drm_atomic_helper_commit_planes() for a discussion of
+	 * the tradeoffs and variants of plane commit helpers.
+	 *
+	 * This callback is used by the atomic modeset helpers, but it is
+	 * optional. If implemented, @atomic_enable should be the inverse of
+	 * @atomic_disable. Drivers that don't want to use either can still
+	 * implement the complete plane update in @atomic_update.
+	 */
+	void (*atomic_enable)(struct drm_plane *plane,
+			      struct drm_atomic_state *state);
+
 	/**
 	 * @atomic_disable:
 	 *
@@ -1351,7 +1377,8 @@ struct drm_plane_helper_funcs {
 	 * the tradeoffs and variants of plane commit helpers.
 	 *
 	 * This callback is used by the atomic modeset helpers and by the
-	 * transitional plane helpers, but it is optional.
+	 * transitional plane helpers, but it is optional. It's intended to
+	 * reverse the effects of @atomic_enable.
 	 */
 	void (*atomic_disable)(struct drm_plane *plane,
 			       struct drm_atomic_state *state);