[PATCH 6.8 305/336] drm/amd/display: Handle Y carry-over in VCP X.Y calculation

Greg Kroah-Hartman
2024-05-14T10:53:08Z

From: George Shen <george.shen@amd.com>

commit 719564737a9ac3d0b49c314450b56cf6f7d71358 upstream.

Theoretically rare corner case where ceil(Y) results in rounding up to
an integer. If this happens, the 1 should be carried over to the X
value.

CC: stable@vger.kernel.org
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: George Shen <george.shen@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/gpu/drm/amd/display/dc/dcn31/dcn31_hpo_dp_link_encoder.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/drivers/gpu/drm/amd/display/dc/dcn31/dcn31_hpo_dp_link_encoder.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn31/dcn31_hpo_dp_link_encoder.c
@@ -395,6 +395,12 @@ void dcn31_hpo_dp_link_enc_set_throttled
x),
25));

+ // If y rounds up to integer, carry it over to x.
+ if (y >> 25) {
+ x += 1;
+ y = 0;
+ }
+
switch (stream_encoder_inst) {
case 0:
REG_SET_2(DP_DPHY_SYM32_VC_RATE_CNTL0, 0,