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

["Menon, Nishanth" <nm@ti.com>]

Alexander Shishkin said the following on 12/16/2009 07:32 PM:
> 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@slind.org>
> CC: linux-i2c@vger.kernel.org
> CC: linux-omap@vger.kernel.org
> ---
>  drivers/i2c/busses/i2c-omap.c |    7 ++++++-
>  1 files changed, 6 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
> index ad8242a..b474c20 100644
> --- a/drivers/i2c/busses/i2c-omap.c
> +++ b/drivers/i2c/busses/i2c-omap.c
> @@ -678,7 +678,9 @@ omap_i2c_rev1_isr(int this_irq, void *dev_id)
>   */
>  static int omap3430_workaround(struct omap_i2c_dev *dev, u16 *stat, int *err)
>  {
> -	while (!(*stat & OMAP_I2C_STAT_XUDF)) {
> +	unsigned long timeout = 10000;
> +
> +	while (!(*stat & OMAP_I2C_STAT_XUDF && --timeout)) {
>   
a) timeout without using an actual delay is not a good idea - consider 
each OPP - we can go upto 1ghz on 3630,
the actual time for 10000 iterations will depend on the MPU speed.
b) how did you arrive at the 10k iteration limit?

>  		if (*stat & (OMAP_I2C_STAT_NACK | OMAP_I2C_STAT_AL)) {
>  			omap_i2c_ack_stat(dev, *stat & (OMAP_I2C_STAT_XRDY |
>  							OMAP_I2C_STAT_XDR));
> @@ -689,6 +691,9 @@ static int omap3430_workaround(struct omap_i2c_dev *dev, u16 *stat, int *err)
>  		*stat = omap_i2c_read_reg(dev, OMAP_I2C_STAT_REG);
>  	}
>  
> +	if (!timeout)
> +		dev_err(dev->dev, "timeout waiting on XUDF bit\n");
> +
>  	return 0;
>  }
>  
>   
Regards,
Nishanth Menon