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

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Message-ID: <1504797770.5105.7.camel@aj.id.au>
Date:   Fri, 08 Sep 2017 01:22:50 +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 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.

Andrew
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