drm/plane-helper: Add a drm_plane_helper_atomic_check() helper

Provides a default plane state check handler for primary planes that are a
fullscreen scanout buffer and whose state scale and position can't change.

There are some drivers that duplicate this logic in their helpers, such as
simpledrm and ssd130x. Factor out this common code into a plane helper and
make drivers use it.

Suggested-by: Thomas Zimmermann <[e-mail]>
Signed-off-by: Javier Martinez Canillas <[e-mail]>
Reviewed-by: Thomas Zimmermann <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_plane_helper.c

···
 	kfree(plane);
 }
 EXPORT_SYMBOL(drm_plane_helper_destroy);
+
+/**
+ * drm_plane_helper_atomic_check() - Helper to check plane atomic-state
+ * @plane: plane to check
+ * @state: atomic state object
+ *
+ * Provides a default plane-state check handler for planes whose atomic-state
+ * scale and positioning are not expected to change since the plane is always
+ * a fullscreen scanout buffer.
+ *
+ * This is often the case for the primary plane of simple framebuffers.
+ *
+ * RETURNS:
+ * Zero on success, or an errno code otherwise.
+ */
+int drm_plane_helper_atomic_check(struct drm_plane *plane, struct drm_atomic_state *state)
+{
+	struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(state, plane);
+	struct drm_crtc *new_crtc = new_plane_state->crtc;
+	struct drm_crtc_state *new_crtc_state = NULL;
+
+	if (new_crtc)
+		new_crtc_state = drm_atomic_get_new_crtc_state(state, new_crtc);
+
+	return drm_atomic_helper_check_plane_state(new_plane_state, new_crtc_state,
+						   DRM_PLANE_NO_SCALING,
+						   DRM_PLANE_NO_SCALING,
+						   false, false);
+}
+EXPORT_SYMBOL(drm_plane_helper_atomic_check);

drivers/gpu/drm/solomon/ssd130x.c

···
 	return ret;
 }
 
-static int ssd130x_primary_plane_helper_atomic_check(struct drm_plane *plane,
-						     struct drm_atomic_state *new_state)
-{
-	struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(new_state, plane);
-	struct drm_crtc *new_crtc = new_plane_state->crtc;
-	struct drm_crtc_state *new_crtc_state = NULL;
-
-	if (new_crtc)
-		new_crtc_state = drm_atomic_get_new_crtc_state(new_state, new_crtc);
-
-	return drm_atomic_helper_check_plane_state(new_plane_state, new_crtc_state,
-						   DRM_PLANE_NO_SCALING,
-						   DRM_PLANE_NO_SCALING,
-						   false, false);
-}
-
 static void ssd130x_primary_plane_helper_atomic_update(struct drm_plane *plane,
 						       struct drm_atomic_state *old_state)
 {
···
 
 static const struct drm_plane_helper_funcs ssd130x_primary_plane_helper_funcs = {
 	DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
-	.atomic_check = ssd130x_primary_plane_helper_atomic_check,
+	.atomic_check = drm_plane_helper_atomic_check,
 	.atomic_update = ssd130x_primary_plane_helper_atomic_update,
 	.atomic_disable = ssd130x_primary_plane_helper_atomic_disable,
 };

drivers/gpu/drm/tiny/simpledrm.c

···
 	DRM_FORMAT_MOD_INVALID
 };
 
-static int simpledrm_primary_plane_helper_atomic_check(struct drm_plane *plane,
-						       struct drm_atomic_state *new_state)
-{
-	struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(new_state, plane);
-	struct drm_crtc *new_crtc = new_plane_state->crtc;
-	struct drm_crtc_state *new_crtc_state = NULL;
-	int ret;
-
-	if (new_crtc)
-		new_crtc_state = drm_atomic_get_new_crtc_state(new_state, new_crtc);
-
-	ret = drm_atomic_helper_check_plane_state(new_plane_state, new_crtc_state,
-						  DRM_PLANE_NO_SCALING,
-						  DRM_PLANE_NO_SCALING,
-						  false, false);
-	if (ret)
-		return ret;
-	else if (!new_plane_state->visible)
-		return 0;
-
-	return 0;
-}
-
 static void simpledrm_primary_plane_helper_atomic_update(struct drm_plane *plane,
 							 struct drm_atomic_state *old_state)
 {
···
 
 static const struct drm_plane_helper_funcs simpledrm_primary_plane_helper_funcs = {
 	DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
-	.atomic_check = simpledrm_primary_plane_helper_atomic_check,
+	.atomic_check = drm_plane_helper_atomic_check,
 	.atomic_update = simpledrm_primary_plane_helper_atomic_update,
 	.atomic_disable = simpledrm_primary_plane_helper_atomic_disable,
 };

include/drm/drm_plane_helper.h

···
 int drm_plane_helper_disable_primary(struct drm_plane *plane,
 				     struct drm_modeset_acquire_ctx *ctx);
 void drm_plane_helper_destroy(struct drm_plane *plane);
+int drm_plane_helper_atomic_check(struct drm_plane *plane, struct drm_atomic_state *state);
 
 #endif