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Subject[PATCH AUTOSEL 5.4 10/52] drm/amd/display: Reset steer fifo before unblanking the stream
Date
From: Nikola Cornij <nikola.cornij@amd.com>

[ Upstream commit 87de6cb2f28153bc74d0a001ca099c29453e145f ]

[why]
During mode transition steer fifo could overflow. Quite often it
recovers by itself, but sometimes it doesn't.

[how]
Add steer fifo reset before unblanking the stream. Also add a short
delay when resetting dig resync fifo to make sure register writes
don't end up back-to-back, in which case the HW might miss the reset
request.

Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
.../drm/amd/display/dc/dcn20/dcn20_stream_encoder.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_stream_encoder.c b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_stream_encoder.c
index 5ab9d62404981..e95025b1d14d2 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_stream_encoder.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_stream_encoder.c
@@ -492,15 +492,23 @@ void enc2_stream_encoder_dp_unblank(
DP_VID_N_MUL, n_multiply);
}

- /* set DIG_START to 0x1 to reset FIFO */
+ /* make sure stream is disabled before resetting steer fifo */
+ REG_UPDATE(DP_VID_STREAM_CNTL, DP_VID_STREAM_ENABLE, false);
+ REG_WAIT(DP_VID_STREAM_CNTL, DP_VID_STREAM_STATUS, 0, 10, 5000);

+ /* set DIG_START to 0x1 to reset FIFO */
REG_UPDATE(DIG_FE_CNTL, DIG_START, 1);
+ udelay(1);

/* write 0 to take the FIFO out of reset */

REG_UPDATE(DIG_FE_CNTL, DIG_START, 0);

- /* switch DP encoder to CRTC data */
+ /* switch DP encoder to CRTC data, but reset it the fifo first. It may happen
+ * that it overflows during mode transition, and sometimes doesn't recover.
+ */
+ REG_UPDATE(DP_STEER_FIFO, DP_STEER_FIFO_RESET, 1);
+ udelay(10);

REG_UPDATE(DP_STEER_FIFO, DP_STEER_FIFO_RESET, 0);

--
2.20.1
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