On Saturday 16 September 2017 05:01 AM, Strashko, Grygorii wrote:
>
>
> On 09/14/2017 10:39 AM, 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).
>>
>> 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.
>>
>
> Reviewed-by: Grygorii Strashko <grygorii.strashko@xxxxxx>
>
>> Signed-off-by: Claudio Foellmi <claudio.foellmi@xxxxxxxx>
>> ---
>> Caveat: It turns out I don't have the hardware to fully test the
>> recovery mechanism. My faulty i2c slave device actually pulls down SCL,
>> not SDA (so the recovery will not succeed in my case).
Maybe, you could detect SCL stuck low case by reading status of SCL line
from OMAP_I2C_SYSTEST_REG and then call IP reset (there is nothing much
that can be done) instead of bus recovery.
>> But by directly connecting SDA to ground, I could at least make sure
>> the recovery function gets called after applying this patch.
>>
I had seen flood of XRDY & RRDY interrupts as soon as TMODE is set to
0x3 as part of omap_i2c_prepare_recovery() leading to unusable system.
Did you observe this behavior on your system? Could you mention the
platform on which this experiment done?
>> drivers/i2c/busses/i2c-omap.c | 7 ++++++-
>> 1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
>> index 1ebb5e9..4b25fd1 100644
>> --- a/drivers/i2c/busses/i2c-omap.c
>> +++ b/drivers/i2c/busses/i2c-omap.c
>> @@ -563,8 +563,13 @@ 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 i2c_recover_bus(&omap->adapter);
>> }
>>
>> msleep(1);
>>
>
--
Regards
Vignesh
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