linux-kernel - Re: [PATCH] hwmon: pmbus: Make reg check and clear faults functions return errors

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Message-ID: <f5752c40-4f1a-c6d6-ee4f-8099e802815e@roeck-us.net>
Date:   Thu, 7 Sep 2017 18:26:25 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Andrew Jeffery <andrew@...id.au>
Cc:     linux-hwmon@...r.kernel.org, jdelvare@...e.com, corbet@....net,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        openbmc@...ts.ozlabs.org, joel@....id.au
Subject: Re: [PATCH] hwmon: pmbus: Make reg check and clear faults functions
 return errors

On 09/07/2017 06:02 PM, Andrew Jeffery wrote:
> On Thu, 2017-09-07 at 17:27 -0700, Guenter Roeck wrote:
>> On 09/07/2017 08:22 AM, Andrew Jeffery wrote:
>>> On Thu, 2017-09-07 at 06:40 -0700, Guenter Roeck wrote:
>>>> On 09/06/2017 04:32 PM, Andrew Jeffery wrote:
>>>>
>>>>>>     
>>>>>> Guess I need to dig up my eval board and see if I can reproduce the problem.
>>>>>> Seems you are saying that the problem is always seen when issuing a sequence
>>>>>> of "clear faults" commands on multiple pages ?
>>>>>
>>>>> Yeah. We're also seeing bad behaviour under other command sequences as well,
>>>>> which lead to this hack of a work-around patch[1].
>>>>>
>>>>> I'd be very interested in the results of testing against the eval board. I
>>>>> don't have access to one and it seems Maxim have discontinued them.
>>>>>
>>>>
>>>> Do you have a somewhat reliable means to reproduce the problem ?
>>>
>>> It seems we hit a bunch of problems by just continually
>>> binding/unbinding the driver, if you don't apply that hacky oneshot
>>> retry patch. We can hit problems (in our design?) with something like:
>>>
>>> # cd /sys/bus/i2c/drivers/max31785; \
>>> 	echo $addr > unbind; \
>>> 	while echo $addr > bind; \
>>> 	do echo $addr > unbind; echo -n .; done;
>>>
>>> It should hit issues covered by this patch, as the register checks are
>>> used in the operations used by probe.
>>>
>>
>> Hmm ... I didn't use your driver but my prototype driver which also supports
>> temperature and voltage attributes, so if anything it should create more
>> stress on the chip.
> 
> I did add the temp and voltage attributes...
> 
> Any chance you can give mine a try? I don't know what I would have done
> to invoke this kind of behaviour, so it would be useful to know whether
> or not it happens with one driver but not the other.
> 

Will do.

>>   No error so far, after running the script for a couple
>> of minutes. How long does it take for errors to appear, and how do I see
>> that there is an error ?
> 
> I'm seeing failures after anything from a handful of bind/unbinds, to
> hundreds of bind/unbinds. It seems to vary.
> 
>> Does the driver fail to instantiate ?
> 
> Typically probe fails so the loop exits. It usually gets -EIO and the
> shell spits out "No such device".
> 
> Thanks for testing, it's a useful data point for us hunting down the
> source of our problems.
> 
I aborted the test after ~2,500 loops without error.

Guenter