drm/ttm: allocate dummy_read_page without DMA32 on fail

Some platforms may not have any memory in ZONE_DMA32 and use IOMMU to allow
32-bit-DMA-only device to work. Forcing GFP_DMA32 on dummy_read_page will
fail on such platforms. Retry after fail will get this works on such
platforms.
Signed-off-by: Yangyu Chen <cyy@cyyself.name>
Link: https://patchwork.freedesktop.org/patch/msgid/tencent_8637383EE0A2C7CC870036AAF01909B26A0A@qq.comSigned-off-by: Christian König <christian.koenig@amd.com>

drivers/gpu/drm/ttm/ttm_device.c

@@ -95,11 +95,17 @@ static int ttm_global_init(void)
 	ttm_pool_mgr_init(num_pages);
 	ttm_tt_mgr_init(num_pages, num_dma32);
 
-	glob->dummy_read_page = alloc_page(__GFP_ZERO | GFP_DMA32);
+	glob->dummy_read_page = alloc_page(__GFP_ZERO | GFP_DMA32 |
+					   __GFP_NOWARN);
 
+	/* Retry without GFP_DMA32 for platforms DMA32 is not available */
 	if (unlikely(glob->dummy_read_page == NULL)) {
-		ret = -ENOMEM;
-		goto out;
+		glob->dummy_read_page = alloc_page(__GFP_ZERO);
+		if (unlikely(glob->dummy_read_page == NULL)) {
+			ret = -ENOMEM;
+			goto out;
+		}
+		pr_warn("Using GFP_DMA32 fallback for dummy_read_page\n");
 	}
 
 	INIT_LIST_HEAD(&glob->device_list);