drm/ast: Enable and disable screen in primary-plane functions

Enabling and disabling the screen used to be done in the register
initialization and the DPMS function. None of these places is related
to the screen's output.

Now the primary plane's update and disable functions handle screen
display state. The primary plane can now be switched off without
displaying garbage.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191202111557.15176-3-tzimmermann@suse.de

drivers/gpu/drm/ast/ast_mode.c

@@ -278,12 +278,11 @@ static void ast_set_std_reg(struct drm_crtc *crtc, struct drm_display_mode *mode
 	jreg = stdtable->misc;
 	ast_io_write8(ast, AST_IO_MISC_PORT_WRITE, jreg);
 
-	/* Set SEQ */
+	/* Set SEQ; except Screen Disable field */
 	ast_set_index_reg(ast, AST_IO_SEQ_PORT, 0x00, 0x03);
-	for (i = 0; i < 4; i++) {
+	ast_set_index_reg_mask(ast, AST_IO_SEQ_PORT, 0x01, 0xdf, stdtable->seq[0]);
+	for (i = 1; i < 4; i++) {
 		jreg = stdtable->seq[i];
-		if (!i)
-			jreg |= 0x20;
 		ast_set_index_reg(ast, AST_IO_SEQ_PORT, (i + 1) , jreg);
 	}
 
@@ -562,28 +561,38 @@ int ast_primary_plane_helper_atomic_check(struct drm_plane *plane,
 void ast_primary_plane_helper_atomic_update(struct drm_plane *plane,
 					    struct drm_plane_state *old_state)
 {
+	struct ast_private *ast = plane->dev->dev_private;
 	struct drm_plane_state *state = plane->state;
 	struct drm_crtc *crtc = state->crtc;
 	struct drm_gem_vram_object *gbo;
 	s64 gpu_addr;
 
-	if (!crtc || !state->fb)
-		return;
-
 	gbo = drm_gem_vram_of_gem(state->fb->obj[0]);
 	gpu_addr = drm_gem_vram_offset(gbo);
 	if (WARN_ON_ONCE(gpu_addr < 0))
 		return; /* Bug: we didn't pin the BO to VRAM in prepare_fb. */
 
 	ast_set_offset_reg(crtc);
 	ast_set_start_address_crt1(crtc, (u32)gpu_addr);
+
+	ast_set_index_reg_mask(ast, AST_IO_SEQ_PORT, 0x1, 0xdf, 0x00);
+}
+
+static void
+ast_primary_plane_helper_atomic_disable(struct drm_plane *plane,
+					struct drm_plane_state *old_state)
+{
+	struct ast_private *ast = plane->dev->dev_private;
+
+	ast_set_index_reg_mask(ast, AST_IO_SEQ_PORT, 0x1, 0xdf, 0x20);
 }
 
 static const struct drm_plane_helper_funcs ast_primary_plane_helper_funcs = {
 	.prepare_fb = drm_gem_vram_plane_helper_prepare_fb,
 	.cleanup_fb = drm_gem_vram_plane_helper_cleanup_fb,
 	.atomic_check = ast_primary_plane_helper_atomic_check,
 	.atomic_update = ast_primary_plane_helper_atomic_update,
+	.atomic_disable = ast_primary_plane_helper_atomic_disable,
 };
 
 static const struct drm_plane_funcs ast_primary_plane_funcs = {
@@ -736,19 +745,20 @@ static void ast_crtc_dpms(struct drm_crtc *crtc, int mode)
 	if (ast->chip == AST1180)
 		return;
 
+	/* TODO: Maybe control display signal generation with
+	 *       Sync Enable (bit CR17.7).
+	 */
 	switch (mode) {
 	case DRM_MODE_DPMS_ON:
 	case DRM_MODE_DPMS_STANDBY:
 	case DRM_MODE_DPMS_SUSPEND:
-		ast_set_index_reg_mask(ast, AST_IO_SEQ_PORT, 0x1, 0xdf, 0);
 		if (ast->tx_chip_type == AST_TX_DP501)
 			ast_set_dp501_video_output(crtc->dev, 1);
 		ast_crtc_load_lut(crtc);
 		break;
 	case DRM_MODE_DPMS_OFF:
 		if (ast->tx_chip_type == AST_TX_DP501)
 			ast_set_dp501_video_output(crtc->dev, 0);
-		ast_set_index_reg_mask(ast, AST_IO_SEQ_PORT, 0x1, 0xdf, 0x20);
 		break;
 	}
 }