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Subject[ 22/69] can: c_can: fix an interrupt thrash issue with c_can driver
3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: AnilKumar Ch <anilkumar@ti.com>

commit 148c87c89e1a8863d3d965179f3ab1a06490569e upstream.

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.

Signed-off-by: AnilKumar Ch <anilkumar@ti.com>
Acked-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/net/can/c_can/c_can.c | 7 +++----
drivers/net/can/c_can/c_can.h | 1 +
2 files changed, 4 insertions(+), 4 deletions(-)

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);



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