Re: [PATCH v2] i2c: omap: Trigger bus recovery in lockup case

[Vignesh R <vigneshr@ti.com>]

Hi,

On Wednesday 04 October 2017 03:13 PM, Claudio Foellmi wrote:
> A very conservative check for bus activity (to prevent interference
> in multimaster setups) prevented the bus recovery methods from being
> triggered in the case that SDA or SCL was stuck low.
> This defeats the purpose of the recovery mechanism, which was introduced
> for exactly this situation (a slave device keeping SDA pulled down).
> 
> Also added a check to make sure SDA is low before attempting recovery.
> If SDA is not stuck low, recovery will not help, so we can skip it.
> 
> Note that bus lockups can persist across reboots. The only other options
> are to reset or power cycle the offending slave device, and many i2c
> slaves do not even have a reset pin.
> 
> If we see that one of the lines is low for the entire timeout duration,
> we can actually be sure that there is no other master driving the bus.
> It is therefore save for us to attempt a bus recovery.
> 
> Signed-off-by: Claudio Foellmi <claudio.foellmi@ergon.ch>
> Cc: Grygorii Strashko <grygorii.strashko@ti.com>
> Cc: Vignesh R <vigneshr@ti.com>
> ---
> Changes since v1:
> Added a check before all bus recoveries, to make sure SDA actually is
> low. This should prevent most unnecessary attempts, which are not
> without risk.
> 

Thanks for the patch! This fixes my case. I no longer see recovery
attempt or IRQ flood:
Tested-by: Vignesh R <vigneshr@ti.com>

Regards
Vignesh

> The full discussion of v1 can be found at
> http://patchwork.ozlabs.org/patch/813889/
> 
>  drivers/i2c/busses/i2c-omap.c | 25 +++++++++++++++++++++++--
>  1 file changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
> index 1ebb5e9..8cdf40a 100644
> --- a/drivers/i2c/busses/i2c-omap.c
> +++ b/drivers/i2c/busses/i2c-omap.c
> @@ -473,6 +473,22 @@ static int omap_i2c_init(struct omap_i2c_dev *omap)
>  }
>  
>  /*
> + * Try bus recovery, but only if SDA is actually low.
> + */
> +static int omap_i2c_recover_bus(struct omap_i2c_dev *omap)
> +{
> +	u16 systest;
> +
> +	systest = omap_i2c_read_reg(omap, OMAP_I2C_SYSTEST_REG);
> +	if ((systest & OMAP_I2C_SYSTEST_SCL_I_FUNC) &&
> +	    (systest & OMAP_I2C_SYSTEST_SDA_I_FUNC))
> +		return 0; /* bus seems to already be fine */
> +	if (!(systest & OMAP_I2C_SYSTEST_SCL_I_FUNC))
> +		return -ETIMEDOUT; /* recovery would not fix SCL */
> +	return i2c_recover_bus(&omap->adapter);
> +}
> +
> +/*
>   * Waiting on Bus Busy
>   */
>  static int omap_i2c_wait_for_bb(struct omap_i2c_dev *omap)
> @@ -482,7 +498,7 @@ static int omap_i2c_wait_for_bb(struct omap_i2c_dev *omap)
>  	timeout = jiffies + OMAP_I2C_TIMEOUT;
>  	while (omap_i2c_read_reg(omap, OMAP_I2C_STAT_REG) & OMAP_I2C_STAT_BB) {
>  		if (time_after(jiffies, timeout))
> -			return i2c_recover_bus(&omap->adapter);
> +			return omap_i2c_recover_bus(omap);
>  		msleep(1);
>  	}
>  
> @@ -563,8 +579,13 @@ static int omap_i2c_wait_for_bb_valid(struct omap_i2c_dev *omap)
>  		}
>  
>  		if (time_after(jiffies, timeout)) {
> +			/*
> +			 * SDA or SCL were low for the entire timeout without
> +			 * any activity detected. Most likely, a slave is
> +			 * locking up the bus with no master driving the clock.
> +			 */
>  			dev_warn(omap->dev, "timeout waiting for bus ready\n");
> -			return -ETIMEDOUT;
> +			return omap_i2c_recover_bus(omap);
>  		}
>  
>  		msleep(1);
> 

-- 
Regards
Vignesh