linux-kernel - [PATCH] drm/meson: Reduce the FIFO lines held when AFBC is not used

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Message-Id: <20221216-afbc_s905x-v1-0-033bebf780d9@baylibre.com>
Date:   Mon, 19 Dec 2022 09:43:05 +0100
From:   Carlo Caione <ccaione@...libre.com>
To:     David Airlie <airlied@...il.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Kevin Hilman <khilman@...libre.com>,
        Neil Armstrong <neil.armstrong@...aro.org>
Cc:     linux-amlogic@...ts.infradead.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Carlo Caione <ccaione@...libre.com>
Subject: [PATCH] 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.

Signed-off-by: Carlo Caione <ccaione@...libre.com>
---
Fix display issues for amlogic SoCs not using AFBC

In 24e0d4058eff the number of lines held after VSYNC was incremented to give
time to the AFBC decoder to do its job. This is causing an issue (seen on
S905x) where the image (on some panels) is dislayed with a vertical offset.
With this patch we try to keep the fix only when AFBC is actually used
filtering on the SoC type.

To: Neil Armstrong <neil.armstrong@...aro.org>
To: David Airlie <airlied@...il.com>
To: Daniel Vetter <daniel@...ll.ch>
To: Kevin Hilman <khilman@...libre.com>
To: Jerome Brunet <jbrunet@...libre.com>
To: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc: dri-devel@...ts.freedesktop.org
Cc: linux-amlogic@...ts.infradead.org
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org
---
 drivers/gpu/drm/meson/meson_viu.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/meson/meson_viu.c b/drivers/gpu/drm/meson/meson_viu.c
index d4b907889a21..cd399b0b7181 100644
--- a/drivers/gpu/drm/meson/meson_viu.c
+++ b/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));

---
base-commit: 84e57d292203a45c96dbcb2e6be9dd80961d981a
change-id: 20221216-afbc_s905x-4baf5fdc9970

Best regards,
-- 
Carlo Caione