github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-07-28 01:55:51 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

drm/amd/display: Fix unsigned underflow in SubVP vblank schedulability check v2

Browse Source 
subvp_vblank_schedulable() checks whether the SubVP active region can
fit the prefetch time, vblank frame time, and the larger of the vblank
blanking time and MALL region.

Commit 11236ac905 ("drm/amd/display: Fix dml2_0 narrowing boundaries")
changed the intermediate timing variables from u16 to u32. After that
change, the schedulability test:

	subvp_active_us - prefetch_us - vblank_frame_us -
	max_vblank_mallregion > 0

is evaluated in unsigned arithmetic. If the required time exceeds the
available active time, the subtraction can underflow and wrap, producing
a large positive value instead of a negative result.

Fix this by comparing the available time against the required time
directly, using u64 for the accumulated required duration.

v2:
- Use uint64_t instead of u64 for consistency with DC style (Dillon)
- Make all terms explicitly uint64_t in the accumulated sum & use
  single-definition form for required_us (Gaghik)

Fixes: 11236ac905 ("drm/amd/display: Fix dml2_0 narrowing boundaries")
Reported-by: Dan Carpenter <error27@gmail.com>
Cc: Roman Li <roman.li@amd.com>
Cc: Alex Hung <alex.hung@amd.com>
Cc: Tom Chung <chiahsuan.chung@amd.com>
Cc: Dillon Varone <dillon.varone@amd.com>
Cc: Gaghik Khachatrian <gaghik.khachatrian@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Cc: Chenyu Chen <chen-yu.chen@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Srinivasan Shanmugam 2026-04-23 19:02:10 +05:30 committed by Alex Deucher
parent 506e047aed
commit 437cbca5ea
1 changed files with 4 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
drivers/gpu/drm/amd/display/dc/dml2_0/dml2_mall_phantom.c
View File

@ -594,11 +594,14 @@ static bool subvp_vblank_schedulable(struct dml2_context *ctx, struct dc_state *
subvp_active_us = (uint32_t)(main_timing->v_addressable * main_timing->h_total /
(double)(main_timing->pix_clk_100hz * 100) * 1000000);
max_vblank_mallregion = vblank_blank_us > mall_region_us ? vblank_blank_us : mall_region_us;
const uint64_t required_us = (uint64_t)prefetch_us +
(uint64_t)vblank_frame_us +
(uint64_t)max_vblank_mallregion;
// Schedulable if VACTIVE region of the SubVP pipe can fit the MALL prefetch, VBLANK frame time,
// and the max of (VBLANK blanking time, MALL region)
// TODO: Possibly add some margin (i.e. the below conditions should be [...] > X instead of [...] > 0)
if (subvp_active_us - prefetch_us - vblank_frame_us - max_vblank_mallregion > 0)
if ((uint64_t)subvp_active_us > required_us)
schedulable = true;
}
return schedulable;