linux-kernel - Re: [PATCH v4 1/1] i2c: algo-pca: Reapply i2c bus settings after reset

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Message-ID: <61c139a0-26fc-8cd1-0b54-b7cb9d9c0648@alliedtelesis.co.nz>
Date:   Sun, 13 Sep 2020 21:23:07 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Wolfram Sang <wsa@...nel.org>
CC:     Evan Nimmo <Evan.Nimmo@...iedtelesis.co.nz>,
        "andriy.shevchenko@...ux.intel.com" 
        <andriy.shevchenko@...ux.intel.com>,
        "jarkko.nikula@...ux.intel.com" <jarkko.nikula@...ux.intel.com>,
        "jdelvare@...e.de" <jdelvare@...e.de>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/1] i2c: algo-pca: Reapply i2c bus settings after
 reset


On 12/09/20 7:45 am, Wolfram Sang wrote:
> On Wed, Sep 09, 2020 at 08:39:50PM +0000, Chris Packham wrote:
>> On 9/09/20 8:23 pm, Wolfram Sang wrote:
>>> On Wed, Sep 09, 2020 at 08:32:47AM +1200, Evan Nimmo wrote:
>>>> If something goes wrong (such as the SCL being stuck low) then we need
>>>> to reset the PCA chip. The issue with this is that on reset we lose all
>>>> config settings and the chip ends up in a disabled state which results
>>>> in a lock up/high CPU usage. We need to re-apply any configuration that
>>>> had previously been set and re-enable the chip.
>>>>
>>>> Signed-off-by: Evan Nimmo <evan.nimmo@...iedtelesis.co.nz>
>>>> Reviewed-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
>>>> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
>>>> Reviewed-by: Wolfram Sang <wsa@...nel.org>
>>> Applied to for-current, thanks!
>>>
>>> For the record, were you able to test both, PCA9564 and PCA9665?
>>>
>> Our hardware platforms only have PCA9665 so that's all we can test.
> Okay, good to know. BTW, just after I sent out my pull request
> containing this patch, I noticed there is no Fixes: tag. So, if you want
> this patch to be backported, please send it to stable@ once my
> pull-request is in Linus' tree.

For our purposes being in Linus's tree is good enough. We've already 
back-ported it to our kernel fork (which doesn't really track any of the 
stable branches properly).

I'm happy to route it to stable@ if you think it's worth it but I don't 
think there's a specific Fixes: reference that can be used. The current 
behavior appears to have been that way since before git (looks like we 
noticed in 2014 but it's taken me 6 years to nag people into sending 
their fixes upstream).