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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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