[PATCH 3/6] net: macb: always use DMA_BIDIRECTIONAL on page pool buffers

["Théo Lebrun" <theo.lebrun@bootlin.com>]

Creating a page pool on open requires knowing the DMA direction. We want
BIDI if an XDP program is loaded (because it might modify and XDP_TX the
buffer) and only need FROM_DEVICE otherwise.

However, we do not reopen on .ndo_bpf() to load an XDP program. This
means the DMA direction might be wrong. Options:
 - Reopen on XDP program load if no program was loaded before.
 - Always use BIDI.

Option 2 shows no reproducible performance costs on my target. It
implies an additional dma_sync_single_for_device() when page pool
buffers are recycled; see __page_pool_put_page().

Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
---
 drivers/net/ethernet/cadence/macb_main.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index 918eee5c8a5b..05bbbaf260ce 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -1582,7 +1582,7 @@ static int gem_rx(struct macb_queue *queue, struct napi_struct *napi,
 
 		dma_sync_single_for_cpu(&bp->pdev->dev,
 					addr, bp->rx_buffer_size,
-					page_pool_get_dma_dir(queue->page_pool));
+					DMA_BIDIRECTIONAL);
 		/* Ensure ctrl is at least as up-to-date as rxused */
 		dma_rmb();
 
@@ -2867,9 +2867,7 @@ static int gem_create_page_pool(struct macb_queue *queue, int qid)
 		.flags = PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV,
 		.pool_size = queue->bp->rx_ring_size,
 		.nid = NUMA_NO_NODE,
-		.dma_dir = rcu_access_pointer(queue->bp->prog)
-				? DMA_BIDIRECTIONAL
-				: DMA_FROM_DEVICE,
+		.dma_dir = DMA_BIDIRECTIONAL,
 		.dev = &queue->bp->pdev->dev,
 		.napi = &queue->napi_rx,
 		.max_len = PAGE_SIZE,
-- 
2.53.0