linux-kernel - Re: [RFC v2] lis3lv02d: avoid divide by zero due to unchecked register read

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Message-Id: <201105181803.08972.chunkeey@googlemail.com>
Date:	Wed, 18 May 2011 18:03:08 +0200
From:	Christian Lamparter <chunkeey@...glemail.com>
To:	Éric Piel <eric.piel@...mplin-utc.net>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [RFC v2] lis3lv02d: avoid divide by zero due to unchecked register read

On Wednesday 18 May 2011 17:56:18 Éric Piel wrote:
> Op 18-05-11 17:47, Christian Lamparter schreef:
> > On Tuesday 17 May 2011 23:46:00 Éric Piel wrote:
> >> Op 16-05-11 23:36, Christian Lamparter schreef:
> >>> On Monday 16 May 2011 13:16:46 Éric Piel wrote:
> >>> Do you know how "volatile" this data rate is? If it never changes
> >>> [at least it doesn't here?] then why not read it once in init_device
> >>> and store it in the device context?
> >> It is not normally changing, normally it is set just at init/unsuspend
> >> (where the bios can also interfere sometimes) and when the user changes
> >> it.
> > Uh, "bios can also interfere"... this sounds very bad. At least for
> > my x41t the bios doesn't care about hdaps once the OS is running.
> >
> >> So definitely within the same function it's not going to suddenly
> >> change.
> > a SMM can happen at any time and if a faulty BIOS [likely, since I got
> > a new laptop] is what caused the crash, I wouldn't bet on "const within
> > a function context".
> Yes, at least on the HP laptop I have the bios enjoys re-initialising 
> the hardware at some default value whenever suspend/resume happens.
> 
> >> We could avoid calculating/checking it twice in
> >> lis3lv02d_selftest(). Care to do a third version with this little clean up?
> > I have my doubts, but ok if you say so... Just one thing: need to do some Q&A
> > on the code above, I haven't tested it extensively yet.
> I didn't know about the SMM... well, then let's keep the code as is.
> 
> I'll try to test it on my laptop in the coming days. On which hardware 
> have you tested it?
I've a dv6-6003eg, it's fairly new.

Regards,
	Chr
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