can: c_can: fix an interrupt thrash issue with c_can driver

This patch fixes an interrupt thrash issue with c_can driver.

In c_can_isr() function interrupts are disabled and enabled only in
c_can_poll() function. c_can_isr() & c_can_poll() both read the
irqstatus flag. However, irqstatus is always read as 0 in c_can_poll()
because all C_CAN interrupts are disabled in c_can_isr(). This causes
all interrupts to be re-enabled in c_can_poll() which in turn causes
another interrupt since the event is not really handled. This keeps
happening causing a flood of interrupts.

To fix this, read the irqstatus register in isr and use the same cached
value in the poll function.

Cc: stable@kernel.org # 2.6.39+
Signed-off-by: AnilKumar Ch <anilkumar@ti.com>
Acked-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

diff --git a/drivers/net/can/c_can/c_can.c b/drivers/net/can/c_can/c_can.c
index 9ac28df3c896f3c6ef90b525a36db243f37326f7..fa016214c52f11cf1b739236872d98215dfee31a 100644 (file)
--- a/drivers/net/can/c_can/c_can.c
+++ b/drivers/net/can/c_can/c_can.c
@@ -952,7 +952,7 @@ static int c_can_poll(struct napi_struct *napi, int quota)
        struct net_device *dev = napi->dev;
        struct c_can_priv *priv = netdev_priv(dev);
 
-       irqstatus = priv->read_reg(priv, &priv->regs->interrupt);
+       irqstatus = priv->irqstatus;
        if (!irqstatus)
                goto end;
 
@@ -1030,12 +1030,11 @@ end:
 
 static irqreturn_t c_can_isr(int irq, void *dev_id)
 {
-       u16 irqstatus;
        struct net_device *dev = (struct net_device *)dev_id;
        struct c_can_priv *priv = netdev_priv(dev);
 
-       irqstatus = priv->read_reg(priv, &priv->regs->interrupt);
-       if (!irqstatus)
+       priv->irqstatus = priv->read_reg(priv, &priv->regs->interrupt);
+       if (!priv->irqstatus)
                return IRQ_NONE;
 
        /* disable all interrupts and schedule the NAPI */

diff --git a/drivers/net/can/c_can/c_can.h b/drivers/net/can/c_can/c_can.h
index 9b7fbef3d09a1248cda69974ac9c3cc4cf9e464e..5f32d34af507e7a9d51c4b37f8add3cd6ff0ddcb 100644 (file)
--- a/drivers/net/can/c_can/c_can.h
+++ b/drivers/net/can/c_can/c_can.h
@@ -76,6 +76,7 @@ struct c_can_priv {
        unsigned int tx_next;
        unsigned int tx_echo;
        void *priv;             /* for board-specific data */
+       u16 irqstatus;
 };
 
 struct net_device *alloc_c_can_dev(void);