net: stmmac: Sync RX Buffer upon allocation

With recent changes that introduced support for Page Pool in stmmac, Jon
reported that NFS boot was no longer working on an ARM64 based platform
that had the IP behind an IOMMU.

As Page Pool API does not guarantee DMA syncing because of the use of
DMA_ATTR_SKIP_CPU_SYNC flag, we have to explicit sync the whole buffer upon
re-allocation because we are always re-using same pages.

In fact, ARM64 code invalidates the DMA area upon two situations [1]:
	- sync_single_for_cpu(): Invalidates if direction != DMA_TO_DEVICE
	- sync_single_for_device(): Invalidates if direction == DMA_FROM_DEVICE

So, as we must invalidate both the current RX buffer and the newly allocated
buffer we propose this fix.

[1] arch/arm64/mm/cache.S
Reported-by: NJon Hunter <jonathanh@nvidia.com>
Tested-by: NJon Hunter <jonathanh@nvidia.com>
Fixes: 2af6106a ("net: stmmac: Introducing support for Page Pool")
Signed-off-by: NJose Abreu <joabreu@synopsys.com>
Tested-by: NEzequiel Garcia <ezequiel@collabora.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -3271,9 +3271,11 @@ static inline int stmmac_rx_threshold_count(struct stmmac_rx_queue *rx_q)
 static inline void stmmac_rx_refill(struct stmmac_priv *priv, u32 queue)
 {
 	struct stmmac_rx_queue *rx_q = &priv->rx_queue[queue];
-	int dirty = stmmac_rx_dirty(priv, queue);
+	int len, dirty = stmmac_rx_dirty(priv, queue);
 	unsigned int entry = rx_q->dirty_rx;
 
+	len = DIV_ROUND_UP(priv->dma_buf_sz, PAGE_SIZE) * PAGE_SIZE;
+
 	while (dirty-- > 0) {
 		struct stmmac_rx_buffer *buf = &rx_q->buf_pool[entry];
 		struct dma_desc *p;
@@ -3291,6 +3293,13 @@ static inline void stmmac_rx_refill(struct stmmac_priv *priv, u32 queue)
 		}
 
 		buf->addr = page_pool_get_dma_addr(buf->page);
+
+		/* Sync whole allocation to device. This will invalidate old
+		 * data.
+		 */
+		dma_sync_single_for_device(priv->device, buf->addr, len,
+					   DMA_FROM_DEVICE);
+
 		stmmac_set_desc_addr(priv, p, buf->addr);
 		stmmac_refill_desc3(priv, rx_q, p);
 
@@ -3425,8 +3434,6 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
 			skb_copy_to_linear_data(skb, page_address(buf->page),
 						frame_len);
 			skb_put(skb, frame_len);
-			dma_sync_single_for_device(priv->device, buf->addr,
-						   frame_len, DMA_FROM_DEVICE);
 
 			if (netif_msg_pktdata(priv)) {
 				netdev_dbg(priv->dev, "frame received (%dbytes)",