drm/mgag200: Implement struct drm_plane_helper_funcs.atomic_enable

Enable the primary plane for mgag200 hardware via atomic_enable.
Atomic helpers invoke this callback only when the plane becomes
active.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230209154107.30680-5-tzimmermann@suse.de

drivers/gpu/drm/mgag200/mgag200_drv.h

@@ -375,12 +375,15 @@ int mgag200_primary_plane_helper_atomic_check(struct drm_plane *plane,
 					      struct drm_atomic_state *new_state);
 void mgag200_primary_plane_helper_atomic_update(struct drm_plane *plane,
 						struct drm_atomic_state *old_state);
+void mgag200_primary_plane_helper_atomic_enable(struct drm_plane *plane,
+						struct drm_atomic_state *state);
 void mgag200_primary_plane_helper_atomic_disable(struct drm_plane *plane,
 						 struct drm_atomic_state *old_state);
 #define MGAG200_PRIMARY_PLANE_HELPER_FUNCS \
 	DRM_GEM_SHADOW_PLANE_HELPER_FUNCS, \
 	.atomic_check = mgag200_primary_plane_helper_atomic_check, \
 	.atomic_update = mgag200_primary_plane_helper_atomic_update, \
+	.atomic_enable = mgag200_primary_plane_helper_atomic_enable, \
 	.atomic_disable = mgag200_primary_plane_helper_atomic_disable
 
 #define MGAG200_PRIMARY_PLANE_FUNCS \

drivers/gpu/drm/mgag200/mgag200_mode.c

@@ -501,7 +501,6 @@ void mgag200_primary_plane_helper_atomic_update(struct drm_plane *plane,
 	struct drm_framebuffer *fb = plane_state->fb;
 	struct drm_atomic_helper_damage_iter iter;
 	struct drm_rect damage;
-	u8 seq1;
 
 	drm_atomic_helper_damage_iter_init(&iter, old_plane_state, plane_state);
 	drm_atomic_for_each_plane_damage(&iter, &damage) {
@@ -511,13 +510,19 @@ void mgag200_primary_plane_helper_atomic_update(struct drm_plane *plane,
 	/* Always scanout image at VRAM offset 0 */
 	mgag200_set_startadd(mdev, (u32)0);
 	mgag200_set_offset(mdev, fb);
+}
+
+void mgag200_primary_plane_helper_atomic_enable(struct drm_plane *plane,
+						struct drm_atomic_state *state)
+{
+	struct drm_device *dev = plane->dev;
+	struct mga_device *mdev = to_mga_device(dev);
+	u8 seq1;
 
-	if (!old_plane_state->crtc && plane_state->crtc) { // enabling
 	RREG_SEQ(0x01, seq1);
 	seq1 &= ~MGAREG_SEQ1_SCROFF;
 	WREG_SEQ(0x01, seq1);
 	msleep(20);
-	}
 }
 
 void mgag200_primary_plane_helper_atomic_disable(struct drm_plane *plane,