drm/meson: Reduce the FIFO lines held when AFBC is not used

Having a bigger number of FIFO lines held after vsync is only useful to
SoCs using AFBC to give time to the AFBC decoder to be reset, configured
and enabled again.

For SoCs not using AFBC this, on the contrary, is causing on some
displays issues and a few pixels vertical offset in the displayed image.

Conditionally increase the number of lines held after vsync only for
SoCs using AFBC, leaving the default value for all the others.

Fixes: 24e0d40 ("drm/meson: hold 32 lines after vsync to give time for AFBC start")
Signed-off-by: Carlo Caione <[email protected]>
Acked-by: Martin Blumenstingl <[email protected]>
Acked-by: Neil Armstrong <[email protected]>
[narmstrong: added fixes tag]
Signed-off-by: Neil Armstrong <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: carlocaione

drivers/gpu/drm/meson/meson_viu.c

@@ -436,15 +436,14 @@ void meson_viu_init(struct meson_drm *priv)
 
 	/* Initialize OSD1 fifo control register */
 	reg = VIU_OSD_DDR_PRIORITY_URGENT |
-		VIU_OSD_HOLD_FIFO_LINES(31) |
 		VIU_OSD_FIFO_DEPTH_VAL(32) | /* fifo_depth_val: 32*8=256 */
 		VIU_OSD_WORDS_PER_BURST(4) | /* 4 words in 1 burst */
 		VIU_OSD_FIFO_LIMITS(2);      /* fifo_lim: 2*16=32 */
 
 	if (meson_vpu_is_compatible(priv, VPU_COMPATIBLE_G12A))
-		reg |= VIU_OSD_BURST_LENGTH_32;
+		reg |= (VIU_OSD_BURST_LENGTH_32 | VIU_OSD_HOLD_FIFO_LINES(31));
 	else
-		reg |= VIU_OSD_BURST_LENGTH_64;
+		reg |= (VIU_OSD_BURST_LENGTH_64 | VIU_OSD_HOLD_FIFO_LINES(4));
 
 	writel_relaxed(reg, priv->io_base + _REG(VIU_OSD1_FIFO_CTRL_STAT));
 	writel_relaxed(reg, priv->io_base + _REG(VIU_OSD2_FIFO_CTRL_STAT));