From: Elad Kanfi <elad...@mellanox.com>
Below is a description of a possible problematic
sequence. CPU-A is sending a frame and CPU-B handles
the interrupt that indicates the frame was sent. CPU-B
reads an invalid value of tx_packet_sent.
CPU-A CPU-B
----- -----
nps_enet_send_frame
.
.
tx_skb = skb
tx_packet_sent = true
order HW to start tx
.
.
HW complete tx
------> get tx complete interrupt
.
.
if(tx_packet_sent == true)
handle tx_skb
end memory transaction
(tx_packet_sent actually
written)
Furthermore there is a dependency between tx_skb and tx_packet_sent.
There is no assurance that tx_skb contains a valid pointer at CPU B
when it sees tx_packet_sent == true.
Solution:
Initialize tx_skb to NULL and use it to indicate that packet was sent,
in this way tx_packet_sent can be removed.
Add a write memory barrier after setting tx_skb in order to make sure
that it is valid before HW is informed and IRQ is fired.
Fixed sequence will be:
CPU-A CPU-B
----- -----
tx_skb = skb
wmb()
.
.
order HW to start tx
.
.
HW complete tx
------> get tx complete interrupt
.
.
if(tx_skb != NULL)
handle tx_skb
tx_skb = NULL
Signed-off-by: Elad Kanfi <elad...@mellanox.com>
Acked-by: Noam Camus <noa...@mellanox.com>
Acked-by: Gilad Ben-Yossef <gila...@mellanox.com>
---
drivers/net/ethernet/ezchip/nps_enet.c | 15 +++++++++------
drivers/net/ethernet/ezchip/nps_enet.h | 2 --
2 files changed, 9 insertions(+), 8 deletions(-)
diff --git a/drivers/net/ethernet/ezchip/nps_enet.c
b/drivers/net/ethernet/ezchip/nps_enet.c
index 1f23845..25ac2de 100644
--- a/drivers/net/ethernet/ezchip/nps_enet.c
+++ b/drivers/net/ethernet/ezchip/nps_enet.c
@@ -145,7 +145,7 @@ static void nps_enet_tx_handler(struct net_device *ndev)
u32 tx_ctrl_nt = (tx_ctrl_value & TX_CTL_NT_MASK) >> TX_CTL_NT_SHIFT;
/* Check if we got TX */
- if (!priv->tx_packet_sent || tx_ctrl_ct)
+ if (!priv->tx_skb || tx_ctrl_ct)
return;
/* Ack Tx ctrl register */
@@ -160,7 +160,7 @@ static void nps_enet_tx_handler(struct net_device *ndev)
}
dev_kfree_skb(priv->tx_skb);
- priv->tx_packet_sent = false;
+ priv->tx_skb = NULL;
if (netif_queue_stopped(ndev))
netif_wake_queue(ndev);
@@ -217,7 +217,7 @@ static irqreturn_t nps_enet_irq_handler(s32 irq, void
*dev_instance)
u32 tx_ctrl_ct = (tx_ctrl_value & TX_CTL_CT_MASK) >> TX_CTL_CT_SHIFT;
u32 rx_ctrl_cr = (rx_ctrl_value & RX_CTL_CR_MASK) >> RX_CTL_CR_SHIFT;
- if ((!tx_ctrl_ct && priv->tx_packet_sent) || rx_ctrl_cr)
+ if ((!tx_ctrl_ct && priv->tx_skb) || rx_ctrl_cr)
if (likely(napi_schedule_prep(&priv->napi))) {
nps_enet_reg_set(priv, NPS_ENET_REG_BUF_INT_ENABLE, 0);
__napi_schedule(&priv->napi);
@@ -387,8 +387,6 @@ static void nps_enet_send_frame(struct net_device *ndev,
/* Write the length of the Frame */
tx_ctrl_value |= length << TX_CTL_NT_SHIFT;
- /* Indicate SW is done */
- priv->tx_packet_sent = true;
tx_ctrl_value |= NPS_ENET_ENABLE << TX_CTL_CT_SHIFT;
/* Send Frame */
nps_enet_reg_set(priv, NPS_ENET_REG_TX_CTL, tx_ctrl_value);
@@ -465,7 +463,7 @@ static s32 nps_enet_open(struct net_device *ndev)
s32 err;
/* Reset private variables */
- priv->tx_packet_sent = false;
+ priv->tx_skb = NULL;
priv->ge_mac_cfg_2_value = 0;
priv->ge_mac_cfg_3_value = 0;
@@ -534,6 +532,11 @@ static netdev_tx_t nps_enet_start_xmit(struct sk_buff *skb,
priv->tx_skb = skb;
+ /* make sure tx_skb is actually written to the memory
+ * before the HW is informed and the IRQ is fired.
+ */
+ wmb();
+
nps_enet_send_frame(ndev, skb);
return NETDEV_TX_OK;
diff --git a/drivers/net/ethernet/ezchip/nps_enet.h
b/drivers/net/ethernet/ezchip/nps_enet.h
index d0cab60..3939ca2 100644
--- a/drivers/net/ethernet/ezchip/nps_enet.h
+++ b/drivers/net/ethernet/ezchip/nps_enet.h
@@ -165,14 +165,12 @@
* struct nps_enet_priv - Storage of ENET's private information.
* @regs_base: Base address of ENET memory-mapped control registers.
* @irq: For RX/TX IRQ number.
- * @tx_packet_sent: SW indication if frame is being sent.
* @tx_skb: socket buffer of sent frame.
* @napi: Structure for NAPI.
*/
struct nps_enet_priv {
void __iomem *regs_base;
s32 irq;
- bool tx_packet_sent;
struct sk_buff *tx_skb;
struct napi_struct napi;
u32 ge_mac_cfg_2_value;
--
1.7.1
