drm/nouveau: fix dma syncing warning with debugging on.

Since I wrote the below patch if you run a debug kernel you can a
dma debug warning like:
nouveau 0000:1f:00.0: DMA-API: device driver tries to sync DMA memory it has not allocated [device address=0x000000016e012000] [size=4096 bytes]

The old nouveau code wasn't consolidate the pages like the ttm code,
but the dma-debug expects the sync code to give it the same base/range
pairs as the allocator.

Fix the nouveau sync code to consolidate pages before calling the
sync code.

Fixes: bd549d35b4 ("nouveau: use ttm populate mapping functions. (v2)")
Reported-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/417588/

drivers/gpu/drm/nouveau/nouveau_bo.c

@@ -547,7 +547,7 @@ nouveau_bo_sync_for_device(struct nouveau_bo *nvbo)
 {
 	struct nouveau_drm *drm = nouveau_bdev(nvbo->bo.bdev);
 	struct ttm_tt *ttm_dma = (struct ttm_tt *)nvbo->bo.ttm;
-	int i;
+	int i, j;
 
 	if (!ttm_dma)
 		return;
@@ -556,10 +556,21 @@ nouveau_bo_sync_for_device(struct nouveau_bo *nvbo)
 	if (nvbo->force_coherent)
 		return;
 
-	for (i = 0; i < ttm_dma->num_pages; i++)
+	for (i = 0; i < ttm_dma->num_pages; ++i) {
+		struct page *p = ttm_dma->pages[i];
+		size_t num_pages = 1;
+
+		for (j = i + 1; j < ttm_dma->num_pages; ++j) {
+			if (++p != ttm_dma->pages[j])
+				break;
+
+			++num_pages;
+		}
 		dma_sync_single_for_device(drm->dev->dev,
 					   ttm_dma->dma_address[i],
-					   PAGE_SIZE, DMA_TO_DEVICE);
+					   num_pages * PAGE_SIZE, DMA_TO_DEVICE);
+		i += num_pages;
+	}
 }
 
 void
@@ -567,7 +578,7 @@ nouveau_bo_sync_for_cpu(struct nouveau_bo *nvbo)
 {
 	struct nouveau_drm *drm = nouveau_bdev(nvbo->bo.bdev);
 	struct ttm_tt *ttm_dma = (struct ttm_tt *)nvbo->bo.ttm;
-	int i;
+	int i, j;
 
 	if (!ttm_dma)
 		return;
@@ -576,9 +587,21 @@ nouveau_bo_sync_for_cpu(struct nouveau_bo *nvbo)
 	if (nvbo->force_coherent)
 		return;
 
-	for (i = 0; i < ttm_dma->num_pages; i++)
+	for (i = 0; i < ttm_dma->num_pages; ++i) {
+		struct page *p = ttm_dma->pages[i];
+		size_t num_pages = 1;
+
+		for (j = i + 1; j < ttm_dma->num_pages; ++j) {
+			if (++p != ttm_dma->pages[j])
+				break;
+
+			++num_pages;
+		}
+
 		dma_sync_single_for_cpu(drm->dev->dev, ttm_dma->dma_address[i],
-					PAGE_SIZE, DMA_FROM_DEVICE);
+					num_pages * PAGE_SIZE, DMA_FROM_DEVICE);
+		i += num_pages;
+	}
 }
 
 void nouveau_bo_add_io_reserve_lru(struct ttm_buffer_object *bo)