[PATCH 17/22] drm/amd/display: Prevent VStartup Overflow

[Tom Chung]

From: Ryan Seto <ryanseto at amd.com>

[Why]
For some VR headsets with large blanks, it's possible
to overflow the OTG_VSTARTUP_PARAM:VSTARTUP_START
register. This can lead to incorrect DML calculations
and underflow downstream.

[How]
Min the calcualted max_vstartup_lines with the max
value of the register.

Reviewed-by: Dillon Varone <dillon.varone at amd.com>
Signed-off-by: Ryan Seto <ryanseto at amd.com>
Signed-off-by: Tom Chung <chiahsuan.chung at amd.com>
---
 .../display/dc/dml2/dml21/src/dml2_core/dml2_core_dcn4_calcs.c  | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_core/dml2_core_dcn4_calcs.c b/drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_core/dml2_core_dcn4_calcs.c
index 4c33d99ca7e8..4c504cb0e1c5 100644
--- a/drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_core/dml2_core_dcn4_calcs.c
+++ b/drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_core/dml2_core_dcn4_calcs.c
@@ -15,6 +15,7 @@
 //#define DML_MODE_SUPPORT_USE_DPM_DRAM_BW
 //#define DML_GLOBAL_PREFETCH_CHECK
 #define ALLOW_SDPIF_RATE_LIMIT_PRE_CSTATE
+#define DML_MAX_VSTARTUP_START 1023
 
 const char *dml2_core_internal_bw_type_str(enum dml2_core_internal_bw_type bw_type)
 {
@@ -3737,6 +3738,7 @@ static unsigned int CalculateMaxVStartup(
 	dml2_printf("DML::%s: vblank_avail = %u\n", __func__, vblank_avail);
 	dml2_printf("DML::%s: max_vstartup_lines = %u\n", __func__, max_vstartup_lines);
 #endif
+	max_vstartup_lines = (unsigned int)math_min2(max_vstartup_lines, DML_MAX_VSTARTUP_START);
 	return max_vstartup_lines;
 }
 
-- 
2.34.1