drm/amdgpu: revert "stop using gart_start as offset for the GTT domain"

Turned out the commit is incomplete and since we remove using the AGP
mapping from the GTT manager it is also not necessary any more.

This reverts commit 22d8bfaf.
Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: James Zhu <James.Zhu@amd.com>
Tested-by: James Zhu <James.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_gtt_mgr.c

@@ -143,8 +143,7 @@ static int amdgpu_gtt_mgr_alloc(struct ttm_mem_type_manager *man,
 	spin_unlock(&mgr->lock);
 
 	if (!r)
-		mem->start = node->node.start +
-			(adev->gmc.gart_start >> PAGE_SHIFT);
+		mem->start = node->node.start;
 
 	return r;
 }

drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c

@@ -188,7 +188,7 @@ static int amdgpu_init_mem_type(struct ttm_bo_device *bdev, uint32_t type,
 	case TTM_PL_TT:
 		/* GTT memory  */
 		man->func = &amdgpu_gtt_mgr_func;
-		man->gpu_offset = 0;
+		man->gpu_offset = adev->gmc.gart_start;
 		man->available_caching = TTM_PL_MASK_CACHING;
 		man->default_caching = TTM_PL_FLAG_CACHED;
 		man->flags = TTM_MEMTYPE_FLAG_MAPPABLE | TTM_MEMTYPE_FLAG_CMA;
@@ -1060,7 +1060,7 @@ static int amdgpu_ttm_backend_bind(struct ttm_tt *ttm,
 	flags = amdgpu_ttm_tt_pte_flags(adev, ttm, bo_mem);
 
 	/* bind pages into GART page tables */
-	gtt->offset = ((u64)bo_mem->start << PAGE_SHIFT) - adev->gmc.gart_start;
+	gtt->offset = (u64)bo_mem->start << PAGE_SHIFT;
 	r = amdgpu_gart_bind(adev, gtt->offset, ttm->num_pages,
 		ttm->pages, gtt->ttm.dma_address, flags);
 
@@ -1112,8 +1112,7 @@ int amdgpu_ttm_alloc_gart(struct ttm_buffer_object *bo)
 		flags = amdgpu_ttm_tt_pte_flags(adev, bo->ttm, &tmp);
 
 		/* Bind pages */
-		gtt->offset = ((u64)tmp.start << PAGE_SHIFT) -
-			adev->gmc.gart_start;
+		gtt->offset = (u64)tmp.start << PAGE_SHIFT;
 		r = amdgpu_ttm_gart_bind(adev, bo, flags);
 		if (unlikely(r)) {
 			ttm_bo_mem_put(bo, &tmp);