From: AnilKumar Ch <anilkumar@ti.com>
Date: Wed, 23 May 2012 12:15:10 +0000 (+0530)
Subject: can: c_can: fix an interrupt thrash issue with c_can driver
X-Git-Tag: v3.5-rc3~22^2~40^2~2
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=148c87c89e1a8863d3d965179f3ab1a06490569e;p=platform%2Fkernel%2Flinux-stable.git

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 9ac28df..fa01621 100644
--- 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 9b7fbef..5f32d34 100644
--- 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);