linux-kernel - [PATCH AUTOSEL 6.13 27/37] drm/amd/display: Prevent VStartup Overflow

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Message-Id: <20250403191513.2680235-27-sashal@kernel.org>
Date: Thu,  3 Apr 2025 15:15:03 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Ryan Seto <ryanseto@....com>,
	Dillon Varone <dillon.varone@....com>,
	Tom Chung <chiahsuan.chung@....com>,
	Daniel Wheeler <daniel.wheeler@....com>,
	Alex Deucher <alexander.deucher@....com>,
	Sasha Levin <sashal@...nel.org>,
	austin.zheng@....com,
	jun.lei@....com,
	harry.wentland@....com,
	sunpeng.li@....com,
	christian.koenig@....com,
	airlied@...il.com,
	simona@...ll.ch,
	siqueira@...lia.com,
	alex.hung@....com,
	colin.i.king@...il.com,
	aurabindo.pillai@....com,
	amd-gfx@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org
Subject: [PATCH AUTOSEL 6.13 27/37] drm/amd/display: Prevent VStartup Overflow

From: Ryan Seto <ryanseto@....com>

[ Upstream commit 29c1c20496a7a9bafe2bc2f833d69aa52e0f2c2d ]

[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@....com>
Signed-off-by: Ryan Seto <ryanseto@....com>
Signed-off-by: Tom Chung <chiahsuan.chung@....com>
Tested-by: Daniel Wheeler <daniel.wheeler@....com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 .../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 ecfa3c898e09d..4285cb7fcbe71 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
@@ -12,6 +12,7 @@
 #define DML2_MAX_FMT_420_BUFFER_WIDTH 4096
 #define DML_MAX_NUM_OF_SLICES_PER_DSC 4
 #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)
 {
@@ -3648,6 +3649,7 @@ 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;
 }
 
-- 
2.39.5