[RFC 1/4] drm/sun4i: Wait for previous mixing process finish before committing next

[roman . stratiienko]

From: Roman Stratiienko <roman.stratiienko@xxxxxxxxxxxxxxx>

Screen composition that requires dynamic layout modification,
especially scaling is corrupted when layout changes.

For example if one of the layer scales down, misaligned lines can be
observed, and dynamic increasing of destination area makes mixer to hang
and draw nothing after drawing modified layer.

After deep investigation it turns that scaler double-buffered registers
are not latched by GLB_DBUFFER bit, instead thay are latched immidiately.

Only way to avoid artifacts is to change the registers after mixer finish
previous frame.

Similar was made in sunxi BSP - scaler register values was stored into RAM,
and moved into registers at sync together with GLB_DBUFFER.

Signed-off-by: Roman Stratiienko <roman.stratiienko@xxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/sun4i/sun8i_mixer.c | 15 +++++++++++++++
 drivers/gpu/drm/sun4i/sun8i_mixer.h |  2 ++
 2 files changed, 17 insertions(+)

diff --git a/drivers/gpu/drm/sun4i/sun8i_mixer.c b/drivers/gpu/drm/sun4i/sun8i_mixer.c
index 8b803eb903b8..eea4813602b7 100644
--- a/drivers/gpu/drm/sun4i/sun8i_mixer.c
+++ b/drivers/gpu/drm/sun4i/sun8i_mixer.c
@@ -257,6 +257,20 @@ const struct de2_fmt_info *sun8i_mixer_format_info(u32 format)
 	return NULL;
 }
 
+static void sun8i_atomic_begin(struct sunxi_engine *engine,
+			       struct drm_crtc_state *old_state)
+{
+	int reg, ret;
+
+	ret = regmap_read_poll_timeout(engine->regs, SUN8I_MIXER_GLOBAL_STATUS,
+				       reg,
+				       !(reg & SUN8I_MIXER_GLOBAL_STATUS_BUSY),
+				       200, 100000);
+
+	if (ret)
+		pr_warn("%s: Wait for frame finish timeout\n", __func__);
+}
+
 static void sun8i_mixer_commit(struct sunxi_engine *engine)
 {
 	DRM_DEBUG_DRIVER("Committing changes\n");
@@ -310,6 +324,7 @@ static struct drm_plane **sun8i_layers_init(struct drm_device *drm,
 static const struct sunxi_engine_ops sun8i_engine_ops = {
 	.commit		= sun8i_mixer_commit,
 	.layers_init	= sun8i_layers_init,
+	.atomic_begin	= sun8i_atomic_begin,
 };
 
 static struct regmap_config sun8i_mixer_regmap_config = {
diff --git a/drivers/gpu/drm/sun4i/sun8i_mixer.h b/drivers/gpu/drm/sun4i/sun8i_mixer.h
index c6cc94057faf..915479cc3077 100644
--- a/drivers/gpu/drm/sun4i/sun8i_mixer.h
+++ b/drivers/gpu/drm/sun4i/sun8i_mixer.h
@@ -25,6 +25,8 @@
 
 #define SUN8I_MIXER_GLOBAL_DBUFF_ENABLE		BIT(0)
 
+#define SUN8I_MIXER_GLOBAL_STATUS_BUSY		BIT(4)
+
 #define DE2_MIXER_UNIT_SIZE			0x6000
 #define DE3_MIXER_UNIT_SIZE			0x3000
 
-- 
2.17.1