netdev - [PATCH net v2 4/9] net: axienet: add missing memory barriers

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Message-Id: <20220112173700.873002-5-robert.hancock@calian.com>
Date:   Wed, 12 Jan 2022 11:36:55 -0600
From:   Robert Hancock <robert.hancock@...ian.com>
To:     netdev@...r.kernel.org
Cc:     radhey.shyam.pandey@...inx.com, davem@...emloft.net,
        kuba@...nel.org, linux-arm-kernel@...ts.infradead.org,
        michal.simek@...inx.com, ariane.keller@....ee.ethz.ch,
        daniel@...earbox.net, Robert Hancock <robert.hancock@...ian.com>
Subject: [PATCH net v2 4/9] net: axienet: add missing memory barriers

This driver was missing some required memory barriers:

Use dma_rmb to ensure we see all updates to the descriptor after we see
that an entry has been completed.

Use wmb and rmb to avoid stale descriptor status between the TX path and
TX complete IRQ path.

Fixes: 8a3b7a252dca9 ("drivers/net/ethernet/xilinx: added Xilinx AXI Ethernet driver")
Signed-off-by: Robert Hancock <robert.hancock@...ian.com>
---
 drivers/net/ethernet/xilinx/xilinx_axienet_main.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
index f4ae035bed35..de8f85175a6c 100644
--- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
+++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
@@ -632,6 +632,8 @@ static int axienet_free_tx_chain(struct net_device *ndev, u32 first_bd,
 		if (nr_bds == -1 && !(status & XAXIDMA_BD_STS_COMPLETE_MASK))
 			break;
 
+		/* Ensure we see complete descriptor update */
+		dma_rmb();
 		phys = desc_get_phys_addr(lp, cur_p);
 		dma_unmap_single(ndev->dev.parent, phys,
 				 (cur_p->cntrl & XAXIDMA_BD_CTRL_LENGTH_MASK),
@@ -645,8 +647,10 @@ static int axienet_free_tx_chain(struct net_device *ndev, u32 first_bd,
 		cur_p->app1 = 0;
 		cur_p->app2 = 0;
 		cur_p->app4 = 0;
-		cur_p->status = 0;
 		cur_p->skb = NULL;
+		/* ensure our transmit path and device don't prematurely see status cleared */
+		wmb();
+		cur_p->status = 0;
 
 		if (sizep)
 			*sizep += status & XAXIDMA_BD_STS_ACTUAL_LEN_MASK;
@@ -704,6 +708,9 @@ static inline int axienet_check_tx_bd_space(struct axienet_local *lp,
 					    int num_frag)
 {
 	struct axidma_bd *cur_p;
+
+	/* Ensure we see all descriptor updates from device or TX IRQ path */
+	rmb();
 	cur_p = &lp->tx_bd_v[(lp->tx_bd_tail + num_frag) % lp->tx_bd_num];
 	if (cur_p->status & XAXIDMA_BD_STS_ALL_MASK)
 		return NETDEV_TX_BUSY;
@@ -843,6 +850,8 @@ static void axienet_recv(struct net_device *ndev)
 
 		tail_p = lp->rx_bd_p + sizeof(*lp->rx_bd_v) * lp->rx_bd_ci;
 
+		/* Ensure we see complete descriptor update */
+		dma_rmb();
 		phys = desc_get_phys_addr(lp, cur_p);
 		dma_unmap_single(ndev->dev.parent, phys, lp->max_frm_size,
 				 DMA_FROM_DEVICE);
-- 
2.31.1