linux-kernel - Re: [PATCH 2/4] i2c: at91: implement i2c bus recovery

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Message-ID: <20200825132846.GA1753@kunai>
Date:   Tue, 25 Aug 2020 15:28:46 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Phil Reid <preid@...ctromag.com.au>
Cc:     Codrin.Ciubotariu@...rochip.com, kamel.bouhara@...tlin.com,
        linux-arm-kernel@...ts.infradead.org, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org, Nicolas.Ferre@...rochip.com,
        alexandre.belloni@...tlin.com, Ludovic.Desroches@...rochip.com,
        devicetree@...r.kernel.org, thomas.petazzoni@...tlin.com
Subject: Re: [PATCH 2/4] i2c: at91: implement i2c bus recovery

Hi Phil,

yes, this thread is old but a similar issue came up again...

On Fri, Oct 25, 2019 at 09:14:00AM +0800, Phil Reid wrote:

> > 
> > > So at the beginning of a new transfer, we should check if SDA (or SCL?)
> > > is low and, if it's true, only then we should try recover the bus.
> > 
> > Yes, this is the proper time to do it. Remember, I2C does not define a
> > timeout.
> > 
> 
> FYI: Just a single poll at the start of the transfer, for it being low, will cause problems with multi-master buses.
> Bus recovery should be attempted after a timeout when trying to communicate, even thou i2c doesn't define a timeout.
> 
> I'm trying to fix the designware drivers handling of this at the moment.

I wonder what you ended up with? You are right, a single poll is not
enough. It only might be if one applies the new "single-master" binding
for a given bus. If that is not present, my best idea so far is to poll
SDA for the time defined in adapter->timeout and if it is all low, then
initiate a recovery.

All the best,

   Wolfram


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