linux-kernel - Re: [PATCH] i2c: tegra: Check for overflow errors with BUG

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Message-ID: <20110815200349.GA2616@legolas.emea.dhcp.ti.com>
Date:	Mon, 15 Aug 2011 23:03:50 +0300
From:	Felipe Balbi <balbi@...com>
To:	Doug Anderson <dianders@...omium.org>
Cc:	balbi@...com, Ben Dooks <ben-linux@...ff.org>,
	Stephen Warren <swarren@...dia.com>,
	Vincent Palatin <vpalatin@...omium.org>,
	Rhyland Klein <rklein@...dia.com>,
	Jean Delvare <khali@...ux-fr.org>,
	Rakesh Iyer <riyer@...dia.com>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] i2c: tegra: Check for overflow errors with BUG_ON.

HI,

On Mon, Aug 15, 2011 at 12:52:36PM -0700, Doug Anderson wrote:
> Felipe,
> 
> On Mon, Aug 15, 2011 at 12:17 PM, Felipe Balbi <balbi@...com> wrote:
> > so due to a FIFO overflow you lock up the whole system ? Can't you e.g.
> > reset the controller and reconfigure it rather than locking up the
> > system ?
> 
> Certainly we could try to be more proactive and reset / retry / return
> the error to the client.  However, since the only expected situation
> where this BUG_ON should hit is due to a bug in this driver itself
> (AKA: i2c clients shouldn't be able to do anything to cause the BUG_ON
> to hit), that seems like a lot of added complexity.

so at least just pass an error to the client, but hanging the entire
system seems a bit too much, dont you think ?

> Also: if there is an arbitrary software bug that causing an overflow
> condition to occur, I'm not sure how stable the system will be.
> Specifically, the i2c controller is used (among other things) to talk
> to the PMU and adjust voltages in the system.  If we just sent it a
> random command, I'd rather report the bug right away so we don't get
> hard to find/reproduce failures in other parts of the system.

that's a good point, I still think that e.g. making a cellphone
unresponsive until a watchdog reset triggers just because you got a FIFO
overflow on the I2C controller is too much.

-- 
balbi

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