[PATCH 1/4] drm/amdgpu/gmc: Fix AMDGPU_GART_PLACEMENT_LOW to not overlap with VRAM

["Timur Kristóf" <timur.kristof@gmail.com>]

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: 917f91d8d8e8 ("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>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c
index 290b9f9043036..f69a931e04fe9 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c
@@ -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:
-- 
2.53.0