[PATCH AUTOSEL 5.10 07/11] drm/amd/display: Fix pixel clock programming

Sasha Levin
2022-08-25T01:43:48Z

From: Ilya Bakoulin <Ilya.Bakoulin@amd.com>

[ Upstream commit 04fb918bf421b299feaee1006e82921d7d381f18 ]

[Why]
Some pixel clock values could cause HDMI TMDS SSCPs to be misaligned
between different HDMI lanes when using YCbCr420 10-bit pixel format.

BIOS functions for transmitter/encoder control take pixel clock in kHz
increments, whereas the function for setting the pixel clock is in 100Hz
increments. Setting pixel clock to a value that is not on a kHz boundary
will cause the issue.

[How]
Round pixel clock down to nearest kHz in 10/12-bpc cases.

Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Brian Chang <Brian.Chang@amd.com>
Signed-off-by: Ilya Bakoulin <Ilya.Bakoulin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c b/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c
index bae3a146b2cc..89cc852cb27c 100644
--- a/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c
+++ b/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c
@@ -546,9 +546,11 @@ static void dce112_get_pix_clk_dividers_helper (
switch (pix_clk_params->color_depth) {
case COLOR_DEPTH_101010:
actual_pixel_clock_100hz = (actual_pixel_clock_100hz * 5) >> 2;
+ actual_pixel_clock_100hz -= actual_pixel_clock_100hz % 10;
break;
case COLOR_DEPTH_121212:
actual_pixel_clock_100hz = (actual_pixel_clock_100hz * 6) >> 2;
+ actual_pixel_clock_100hz -= actual_pixel_clock_100hz % 10;
break;
case COLOR_DEPTH_161616:
actual_pixel_clock_100hz = actual_pixel_clock_100hz * 2;
--
2.35.1