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

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Date:   Wed, 10 Mar 2021 02:19:41 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Guenter Roeck <linux@...ck-us.net>,
        "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 9/03/21 9:27 am, Chris Packham wrote:
> On 8/03/21 5:59 pm, Guenter Roeck wrote:
>> Other than that, the only other real idea I have would be to monitor
>> the i2c bus.
> I am in the fortunate position of being able to go into the office and 
> even happen to have the expensive scope at the moment. Now I just need 
> to find a tame HW engineer so I don't burn myself trying to attach the 
> probes.
One thing I see on the scope is that when there is a CPU load there 
appears to be some clock stretching going on (SCL is held low some 
times). I don't see it without the CPU load. It's hard to correlate a 
clock stretching event with a bad read or error but it is one area where 
the SMBUS spec has a maximum that might cause the device to give up waiting.