[net-next, PATCH, v2] net: netsec: Sync dma for device on buffer allocation

[Ilias Apalodimas <ilias.apalodimas@linaro.org>]

Quoting Arnd,

We have to do a sync_single_for_device /somewhere/ before the
buffer is given to the device. On a non-cache-coherent machine with
a write-back cache, there may be dirty cache lines that get written back
after the device DMA's data into it (e.g. from a previous memset
from before the buffer got freed), so you absolutely need to flush any
dirty cache lines on it first.

Since the coherency is configurable in this device make sure we cover
all configurations by explicitly syncing the allocated buffer for the
device before refilling it's descriptors

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
---

Changes since V1: 
- Make the code more readable
 
 drivers/net/ethernet/socionext/netsec.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/socionext/netsec.c b/drivers/net/ethernet/socionext/netsec.c
index 5544a722543f..ada7626bf3a2 100644
--- a/drivers/net/ethernet/socionext/netsec.c
+++ b/drivers/net/ethernet/socionext/netsec.c
@@ -727,21 +727,26 @@ static void *netsec_alloc_rx_data(struct netsec_priv *priv,
 {
 
 	struct netsec_desc_ring *dring = &priv->desc_ring[NETSEC_RING_RX];
+	enum dma_data_direction dma_dir;
+	dma_addr_t dma_start;
 	struct page *page;
 
 	page = page_pool_dev_alloc_pages(dring->page_pool);
 	if (!page)
 		return NULL;
 
+	dma_start = page_pool_get_dma_addr(page);
 	/* We allocate the same buffer length for XDP and non-XDP cases.
 	 * page_pool API will map the whole page, skip what's needed for
 	 * network payloads and/or XDP
 	 */
-	*dma_handle = page_pool_get_dma_addr(page) + NETSEC_RXBUF_HEADROOM;
+	*dma_handle = dma_start + NETSEC_RXBUF_HEADROOM;
 	/* Make sure the incoming payload fits in the page for XDP and non-XDP
 	 * cases and reserve enough space for headroom + skb_shared_info
 	 */
 	*desc_len = PAGE_SIZE - NETSEC_RX_BUF_NON_DATA;
+	dma_dir = page_pool_get_dma_dir(dring->page_pool);
+	dma_sync_single_for_device(priv->dev, dma_start, PAGE_SIZE, dma_dir);
 
 	return page_address(page);
 }
-- 
2.20.1