drm/amdgpu: Fix the vram base start address

If the size returned by drm buddy allocator is higher than
the required size, we take the higher size to calculate
the buffer start address. This is required if we couldn't
trim the buffer to the requested size. This will fix the
display corruption issue on APU's which has limited VRAM
size.

Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2859
Fixes: 0a1844bf ("drm/buddy: Improve contiguous memory allocation")
Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -77,7 +77,16 @@ static inline bool amdgpu_is_vram_mgr_blocks_contiguous(struct list_head *head)
 	return true;
 }
 
+static inline u64 amdgpu_vram_mgr_blocks_size(struct list_head *head)
+{
+	struct drm_buddy_block *block;
+	u64 size = 0;
 
+	list_for_each_entry(block, head, link)
+		size += amdgpu_vram_mgr_block_size(block);
+
+	return size;
+}
 
 /**
  * DOC: mem_info_vram_total
@@ -516,6 +525,8 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
 	mutex_unlock(&mgr->lock);
 
 	vres->base.start = 0;
+	size = max_t(u64, amdgpu_vram_mgr_blocks_size(&vres->blocks),
+		     vres->base.size);
 	list_for_each_entry(block, &vres->blocks, link) {
 		unsigned long start;
 
@@ -523,8 +534,8 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
 			amdgpu_vram_mgr_block_size(block);
 		start >>= PAGE_SHIFT;
 
-		if (start > PFN_UP(vres->base.size))
-			start -= PFN_UP(vres->base.size);
+		if (start > PFN_UP(size))
+			start -= PFN_UP(size);
 		else
 			start = 0;
 		vres->base.start = max(vres->base.start, start);