netdev - [net-next, PATCH, v3] net: netsec: Sync dma for device on buffer allocation

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Date:   Fri,  5 Jul 2019 13:47:47 +0300
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     netdev@...r.kernel.org, jaswinder.singh@...aro.org
Cc:     brouer@...hat.com, ard.biesheuvel@...aro.org, arnd@...db.de,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>
Subject: [net-next, PATCH, v3] net: netsec: Sync dma for device on buffer allocation

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@...aro.org>
---
Changes since v2:
- Only sync for the portion of the packet owned by the NIC as suggested by 
  Jesper

 drivers/net/ethernet/socionext/netsec.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/ethernet/socionext/netsec.c b/drivers/net/ethernet/socionext/netsec.c
index 5544a722543f..6b954ad88842 100644
--- a/drivers/net/ethernet/socionext/netsec.c
+++ b/drivers/net/ethernet/socionext/netsec.c
@@ -727,6 +727,7 @@ 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;
 	struct page *page;
 
 	page = page_pool_dev_alloc_pages(dring->page_pool);
@@ -742,6 +743,8 @@ static void *netsec_alloc_rx_data(struct netsec_priv *priv,
 	 * 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_handle, *desc_len, dma_dir);
 
 	return page_address(page);
 }
-- 
2.20.1