linux-kernel - Re: [PATCH v3 2/4] i2c: omap: implement workaround for handling invalid BB-bit values

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Date:	Mon, 24 Nov 2014 20:13:47 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Felipe Balbi <balbi@...com>
Cc:	Kevin Hilman <khilman@...nel.org>,
	Alexander Kochetkov <al.kochet@...il.com>,
	Tony Lindgren <tony@...mide.com>,
	linux-omap <linux-omap@...r.kernel.org>,
	linux-i2c@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/4] i2c: omap: implement workaround for handling
 invalid BB-bit values

On Mon, Nov 24, 2014 at 01:10:23PM -0600, Felipe Balbi wrote:
> On Mon, Nov 24, 2014 at 11:08:48AM -0800, Kevin Hilman wrote:
> > On Sat, Nov 22, 2014 at 11:47 AM, Alexander Kochetkov
> > <al.kochet@...il.com> wrote:
> > > In a multimaster environment, after IP software reset, BB-bit value doesn't
> > > correspond to the current bus state. It may happen what BB-bit will be 0,
> > > while the bus is busy due to another I2C master activity.
> > >
> > > Any transfer started when BB=0 and bus is busy wouldn't be completed by IP
> > > and results in controller timeout. More over, in some cases IP could
> > > interrupt another master's transfer and corrupt data on wire.
> > >
> > > The commit implement method allowing to prevent IP from entering into
> > > "controller timeout" state and from "data corruption" state.
> > >
> > > The one drawback is the need to wait for 10ms before the first transfer.
> > >
> > > Tested on Beagleboard XM C.
> > > Tested on BBB and AM437x Starter Kit by Felipe Balbi.
> > >
> > > Signed-off-by: Alexander Kochetkov <al.kochet@...il.com>
> > > Tested-by: Felipe Balbi <balbi@...com>
> > > Reviewed-by: Felipe Balbi <balbi@...com>
> > 
> > This patch recently hit linux-next (as commit 903c3859f77f) and boot
> > breakage[1] in next-20141124 on OMAP3530 Beagle and Overo/Tobi boards
> > was bisected down to this commit.
> > 
> > Kevin
> > 
> > [1] http://status.armcloud.us/boot/?next-20141124&omap
> 
> btw, based on Kevin's boot test, only OMAP3530 is failing.

OK, giving Alexander some time for a fix. If it can't be found, I'll
revert this patch. Thanks!


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