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drm/amdgpu/gmc: Fix AMDGPU_GART_PLACEMENT_LOW to not overlap with VRAM

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When the GART placement is set to AMDGPU_GART_PLACEMENT_LOW:
Make sure that GART does not overlap with VRAM when
VRAM is configured to be in the low address space.

Solve this according to the following logic:
- When GART fits before VRAM, use zero address for GART
- Otherwise, put GART after the end of VRAM, aligned to 4 GiB

Previously, I had assumed this was not possible
so it was OK to not handle it, but now we got a report
from a user who has a board that is configured this way.

Fixes: 917f91d8d8 ("drm/amdgpu/gmc: add a way to force a particular placement for GART")
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 3d9de5d86a1658cadb311461b001eb1df67263ad)
This commit is contained in:
Timur Kristóf 2026-04-18 23:49:30 +02:00 committed by Alex Deucher
parent 87612bab96
commit 36d65da757
1 changed files with 4 additions and 1 deletions
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5
drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c
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@ -314,7 +314,10 @@ void amdgpu_gmc_gart_location(struct amdgpu_device *adev, struct amdgpu_gmc *mc,
mc->gart_start = max_mc_address - mc->gart_size + 1;
break;
case AMDGPU_GART_PLACEMENT_LOW:
mc->gart_start = 0;
if (size_bf >= mc->gart_size)
mc->gart_start = 0;
else
mc->gart_start = ALIGN(mc->fb_end, four_gb);
break;
case AMDGPU_GART_PLACEMENT_BEST_FIT:
default: