2 files changed, 18 insertions, 3 deletions

diff --git a/drivers/net/can/sja1000/sja1000.c b/drivers/net/can/sja1000/sja1000.c
index 24b58619f7c1..85f7cbfe8e5f 100644
--- a/drivers/net/can/sja1000/sja1000.c
+++ b/drivers/net/can/sja1000/sja1000.c
@@ -83,6 +83,20 @@ static struct can_bittiming_const sja1000_bittiming_const = {
         .brp_inc = 1,
 };
 
+static void sja1000_write_cmdreg(struct sja1000_priv *priv, u8 val)
+{
+        unsigned long flags;
+
+        /*
+         * The command register needs some locking and time to settle
+         * the write_reg() operation - especially on SMP systems.
+         */
+        spin_lock_irqsave(&priv->cmdreg_lock, flags);
+        priv->write_reg(priv, REG_CMR, val);
+        priv->read_reg(priv, REG_SR);
+        spin_unlock_irqrestore(&priv->cmdreg_lock, flags);
+}
+
 static int sja1000_probe_chip(struct net_device *dev)
 {
         struct sja1000_priv *priv = netdev_priv(dev);
@@ -294,7 +308,7 @@ static netdev_tx_t sja1000_start_xmit(struct sk_buff *skb,
 
         can_put_echo_skb(skb, dev, 0);
 
-        priv->write_reg(priv, REG_CMR, CMD_TR);
+        sja1000_write_cmdreg(priv, CMD_TR);
 
         return NETDEV_TX_OK;
 }
@@ -343,7 +357,7 @@ static void sja1000_rx(struct net_device *dev)
         cf->can_id = id;
 
         /* release receive buffer */
-        priv->write_reg(priv, REG_CMR, CMD_RRB);
+        sja1000_write_cmdreg(priv, CMD_RRB);
 
         netif_rx(skb);
 
@@ -371,7 +385,7 @@ static int sja1000_err(struct net_device *dev, uint8_t isrc, uint8_t status)
                 cf->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
                 stats->rx_over_errors++;
                 stats->rx_errors++;
-                priv->write_reg(priv, REG_CMR, CMD_CDO);        /* clear bit */
+                sja1000_write_cmdreg(priv, CMD_CDO);    /* clear bit */
         }
 
         if (isrc & IRQ_EI) {
diff --git a/drivers/net/can/sja1000/sja1000.h b/drivers/net/can/sja1000/sja1000.h
index 97a622b9302f..de8e778f6832 100644
--- a/drivers/net/can/sja1000/sja1000.h
+++ b/drivers/net/can/sja1000/sja1000.h
@@ -167,6 +167,7 @@ struct sja1000_priv {
 
         void __iomem *reg_base;  /* ioremap'ed address to registers */
         unsigned long irq_flags; /* for request_irq() */
+        spinlock_t cmdreg_lock;  /* lock for concurrent cmd register writes */
 
         u16 flags;              /* custom mode flags */
         u8 ocr;                 /* output control register */