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

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Date:   Tue, 9 Mar 2021 04:36:47 +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 11:10 am, Chris Packham wrote:
>
> On 8/03/21 5:59 pm, Guenter Roeck wrote:
>> 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.
> Reworking those loops seems to have had a positive result. I'll do a 
> bit more testing and hopefully get a patch out later today.
D'oh my "fix" was to replace the cond_reshed() with msleep(10) which did 
"fix" the problem but made every i2c read slow. I didn't notice when 
testing just the lm81 but as soon as I booted the system with more i2c 
devices I saw stupidly slow boot times.
>>   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