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

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Message-ID: <1504832527.6124.1.camel@aj.id.au>
Date:   Fri, 08 Sep 2017 11:02:07 +1000
From:   Andrew Jeffery <andrew@...id.au>
To:     Guenter Roeck <linux@...ck-us.net>
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 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.

>  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.

Andrew
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