drm/ast: Reload gamma LUT after changing primary plane's color format

The gamma LUT has to be reloaded after changing the primary plane's
color format. This used to be done implicitly by the CRTC atomic_enable()
helper after updating the primary plane. With the recent reordering of
the steps, the primary plane's setup was moved last and invalidated
the gamma LUT. Fix this by setting the LUT from within atomic_flush().
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Fixes: 2f0ddd89 ("drm/ast: Enable CRTC before planes")
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Dave Airlie <airlied@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20200922144655.23624-1-tzimmermann@suse.de
(cherry-picked from 8e3784df)

drivers/gpu/drm/ast/ast_mode.c

@@ -742,7 +742,6 @@ static void ast_crtc_dpms(struct drm_crtc *crtc, int mode)
 	case DRM_MODE_DPMS_SUSPEND:
 		if (ast->tx_chip_type == AST_TX_DP501)
 			ast_set_dp501_video_output(crtc->dev, 1);
-		ast_crtc_load_lut(ast, crtc);
 		break;
 	case DRM_MODE_DPMS_OFF:
 		if (ast->tx_chip_type == AST_TX_DP501)
@@ -777,6 +776,21 @@ static int ast_crtc_helper_atomic_check(struct drm_crtc *crtc,
 	return 0;
 }
 
+static void
+ast_crtc_helper_atomic_flush(struct drm_crtc *crtc, struct drm_crtc_state *old_crtc_state)
+{
+	struct ast_private *ast = to_ast_private(crtc->dev);
+	struct ast_crtc_state *ast_crtc_state = to_ast_crtc_state(crtc->state);
+	struct ast_crtc_state *old_ast_crtc_state = to_ast_crtc_state(old_crtc_state);
+
+	/*
+	 * The gamma LUT has to be reloaded after changing the primary
+	 * plane's color format.
+	 */
+	if (old_ast_crtc_state->format != ast_crtc_state->format)
+		ast_crtc_load_lut(ast, crtc);
+}
+
 static void
 ast_crtc_helper_atomic_enable(struct drm_crtc *crtc,
 			      struct drm_crtc_state *old_crtc_state)
@@ -830,6 +844,7 @@ ast_crtc_helper_atomic_disable(struct drm_crtc *crtc,
 
 static const struct drm_crtc_helper_funcs ast_crtc_helper_funcs = {
 	.atomic_check = ast_crtc_helper_atomic_check,
+	.atomic_flush = ast_crtc_helper_atomic_flush,
 	.atomic_enable = ast_crtc_helper_atomic_enable,
 	.atomic_disable = ast_crtc_helper_atomic_disable,
 };