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SubjectRe: [PATCH] i2c: cadence: Implement timeout
On Wed, Oct 24, 2018 at 04:20:03PM +0530, shubhrajyoti.datta@gmail.com wrote:
> From: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
>
> In some cases we are waiting in a loop. Replace the infinite wait with
> the timeout.
>
> Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
> ---
> drivers/i2c/busses/i2c-cadence.c | 30 ++++++++++++++++++++++++++----
> 1 file changed, 26 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
> index b136057..9c38278 100644
> --- a/drivers/i2c/busses/i2c-cadence.c
> +++ b/drivers/i2c/busses/i2c-cadence.c
> @@ -209,6 +209,7 @@ static irqreturn_t cdns_i2c_isr(int irq, void *ptr)
> struct cdns_i2c *id = ptr;
> /* Signal completion only after everything is updated */
> int done_flag = 0;
> + unsigned int timeout;
> irqreturn_t status = IRQ_NONE;
>
> isr_status = cdns_i2c_readreg(CDNS_I2C_ISR_OFFSET);
> @@ -235,6 +236,7 @@ static irqreturn_t cdns_i2c_isr(int irq, void *ptr)
> ((isr_status & CDNS_I2C_IXR_COMP) ||
> (isr_status & CDNS_I2C_IXR_DATA))) {
> /* Read data if receive data valid is set */
> + timeout = 1000;
> while (cdns_i2c_readreg(CDNS_I2C_SR_OFFSET) &
> CDNS_I2C_SR_RXDV) {
> /*
> @@ -253,6 +255,16 @@ static irqreturn_t cdns_i2c_isr(int irq, void *ptr)
>
> if (cdns_is_holdquirk(id, hold_quirk))
> break;
> + timeout--;
> + if (timeout)
> + mdelay(1);
> + else
> + break;
> + }
> + if (!timeout) {
> + id->err_status = -ETIMEDOUT;
> + complete(&id->xfer_done);
> + return IRQ_HANDLED;

Good kernel programming principle: Always check for the success
condition when exiting due to timeout rather than the fact that we
timed out.

Also, is this _really_ a loop that needs a timeout condition? Looking
at the original code, it looks like the purpose of the loop is to read
more than one byte, and you are introducing a 1ms delay between the
read of each byte.

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