[PATCH 1/3] drm/ast: Do full modeset if the primary plane's format changes

[Thomas Zimmermann]

The atomic modesetting code tried to distinguish format changes from
full modesetting operations. In practice, this was buggy and the format
registers were often updated even for simple pageflips.

Instead do a full modeset if the primary plane changes formats. It's
just as rare as an actual mode change, so there will be no performance
penalty.

The patch also replaces a reference to drm_crtc_state.allow_modeset with
the correct call to drm_atomic_crtc_needs_modeset().

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
Fixes: 4961eb60f145 ("drm/ast: Enable atomic modesetting")
Cc: Thomas Zimmermann <tzimmermann at suse.de>
Cc: Gerd Hoffmann <kraxel at redhat.com>
Cc: Dave Airlie <airlied at redhat.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Sam Ravnborg <sam at ravnborg.org>
Cc: Emil Velikov <emil.l.velikov at gmail.com>
Cc: "Y.C. Chen" <yc_chen at aspeedtech.com>
Cc: <stable at vger.kernel.org> # v5.6+
---
 drivers/gpu/drm/ast/ast_mode.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
index 154cd877d9d1..3680a000b812 100644
--- a/drivers/gpu/drm/ast/ast_mode.c
+++ b/drivers/gpu/drm/ast/ast_mode.c
@@ -527,8 +527,8 @@ static const uint32_t ast_primary_plane_formats[] = {
 static int ast_primary_plane_helper_atomic_check(struct drm_plane *plane,
 						 struct drm_plane_state *state)
 {
-	struct drm_crtc_state *crtc_state;
-	struct ast_crtc_state *ast_crtc_state;
+	struct drm_crtc_state *crtc_state, *old_crtc_state;
+	struct ast_crtc_state *ast_crtc_state, *old_ast_crtc_state;
 	int ret;
 
 	if (!state->crtc)
@@ -550,6 +550,15 @@ static int ast_primary_plane_helper_atomic_check(struct drm_plane *plane,
 
 	ast_crtc_state->format = state->fb->format;
 
+	old_crtc_state = drm_atomic_get_old_crtc_state(state->state, state->crtc);
+	if (!old_crtc_state)
+		return 0;
+	old_ast_crtc_state = to_ast_crtc_state(old_crtc_state);
+	if (!old_ast_crtc_state)
+		return 0;
+	if (ast_crtc_state->format != old_ast_crtc_state->format)
+		crtc_state->mode_changed = true;
+
 	return 0;
 }
 
@@ -775,18 +784,18 @@ static void ast_crtc_helper_atomic_flush(struct drm_crtc *crtc,
 
 	ast_state = to_ast_crtc_state(crtc->state);
 
-	format = ast_state->format;
-	if (!format)
+	if (!drm_atomic_crtc_needs_modeset(crtc->state))
 		return;
 
+	format = ast_state->format;
+	if (drm_WARN_ON_ONCE(dev, !format))
+		return; /* BUG: We didn't set format in primary check(). */
+
 	vbios_mode_info = &ast_state->vbios_mode_info;
 
 	ast_set_color_reg(ast, format);
 	ast_set_vbios_color_reg(ast, format, vbios_mode_info);
 
-	if (!crtc->state->mode_changed)
-		return;
-
 	adjusted_mode = &crtc->state->adjusted_mode;
 
 	ast_set_vbios_mode_reg(ast, adjusted_mode, vbios_mode_info);
-- 
2.27.0