Re: [PATCH v2 2/2] omap i2c: add a timeout to the busy waiting

[Aaro Koskinen <aaro.koskinen-xNZwKgViW5gAvxtiuMwx3w@public.gmane.org>]

Hi,

Alexander Shishkin wrote:
> The errata 1.153 workaround is busy waiting on XUDF bit in interrupt
> context, which may lead to kernel hangs. The problem can be reproduced
> by running the bus with wrong (too high) speed.
> 
> Signed-off-by: Alexander Shishkin <virtuoso-0lOfPCoBze7YtjvyW6yDsg@public.gmane.org>
> Acked-by: Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org>
> CC: linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> CC: linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> CC: nm-l0cyMroinI0@public.gmane.org
> ---
>  drivers/i2c/busses/i2c-omap.c |    8 ++++++++
>  1 files changed, 8 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
> index 2d146ac..7d56a25 100644
> --- a/drivers/i2c/busses/i2c-omap.c
> +++ b/drivers/i2c/busses/i2c-omap.c
> @@ -678,6 +678,8 @@ omap_i2c_rev1_isr(int this_irq, void *dev_id)
>   */
>  static int errata_omap3_1p153(struct omap_i2c_dev *dev, u16 *stat, int *err)
>  {
> +	unsigned long timeout = jiffies + msecs_to_jiffies(1);
> +
>  	while (!(*stat & OMAP_I2C_STAT_XUDF)) {
>  		if (*stat & (OMAP_I2C_STAT_NACK | OMAP_I2C_STAT_AL)) {
>  			omap_i2c_ack_stat(dev, *stat & (OMAP_I2C_STAT_XRDY |
> @@ -685,6 +687,12 @@ static int errata_omap3_1p153(struct omap_i2c_dev *dev, u16 *stat, int *err)
>  			*err |= OMAP_I2C_STAT_XUDF;
>  			return -ETIMEDOUT;
>  		}
> +
> +		if (time_after(jiffies, timeout)) {

This is called from hard interrupt context, so we cannot use jiffies.

> +			dev_err(dev->dev, "timeout waiting on XUDF bit\n");
> +			return 0;
> +		}
> +
>  		cpu_relax();
>  		*stat = omap_i2c_read_reg(dev, OMAP_I2C_STAT_REG);
>  	}

A.