drm/amdgpu: reapply "fix start calculation in amdgpu_vram_mgr_new""

This re-applys commit 5e3f1e77.

The original problem this was reverted for was found and the correct fix
will be merged to drm-misc-next-fixes.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220714132315.587217-1-christian.koenig@amd.com

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

@@ -496,16 +496,22 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
 			list_splice_tail(trim_list, &vres->blocks);
 	}
 
-	list_for_each_entry(block, &vres->blocks, link)
-		vis_usage += amdgpu_vram_mgr_vis_size(adev, block);
+	vres->base.start = 0;
+	list_for_each_entry(block, &vres->blocks, link) {
+		unsigned long start;
 
-	block = amdgpu_vram_mgr_first_block(&vres->blocks);
-	if (!block) {
-		r = -EINVAL;
-		goto error_fini;
-	}
+		start = amdgpu_vram_mgr_block_start(block) +
+			amdgpu_vram_mgr_block_size(block);
+		start >>= PAGE_SHIFT;
 
-	vres->base.start = amdgpu_vram_mgr_block_start(block) >> PAGE_SHIFT;
+		if (start > vres->base.num_pages)
+			start -= vres->base.num_pages;
+		else
+			start = 0;
+		vres->base.start = max(vres->base.start, start);
+
+		vis_usage += amdgpu_vram_mgr_vis_size(adev, block);
+	}
 
 	if (amdgpu_is_vram_mgr_blocks_contiguous(&vres->blocks))
 		vres->base.placement |= TTM_PL_FLAG_CONTIGUOUS;