linux-kernel - Re: Errant readings on LM81 with T2080 SoC

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Message-ID: <5709f180-04b5-09b2-e1c4-53eb5c9345d8@roeck-us.net>
Date:   Sun, 7 Mar 2021 20:59:01 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Chris Packham <Chris.Packham@...iedtelesis.co.nz>,
        "jdelvare@...e.com" <jdelvare@...e.com>
Cc:     "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: Errant readings on LM81 with T2080 SoC

On 3/7/21 8:37 PM, Chris Packham wrote:
[ ... ]
>> That's from -ENXIO which is used in only one place in i2c-mpc.c. I'll 
>> enable some debug and see what we get.
> 
> For the errant readings there was nothing abnormal reported by the driver.
> 
> For the "No such device or address" I saw "mpc-i2c ffe119000.i2c: No 
> RXAK" which matches up with the -ENXIO return.
> 

Id suggest to check the time until not busy and stop in mpc_xfer().
Those hot loops are unusual, and may well mess up the code especially
if preempt is enabled. Also, are you using interrupts or polling in
your system ? The interrupt handler looks a bit odd, with "Read again
to allow register to stabilise".

Do you have fsl,timeout set in the devicetree properties and, if so,
have you played with it ?

Other than that, the only other real idea I have would be to monitor
the i2c bus.

Guenter