linux-kernel - Re: [3.16.1 REGRESSION]: Simtec Entropy Key (cdc-acm) broken in 3.16

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Message-ID: <1410160901.11338.16.camel@linux-fkkt.site>
Date:	Mon, 08 Sep 2014 09:21:41 +0200
From:	Oliver Neukum <oliver@...kum.org>
To:	Nix <nix@...eri.org.uk>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [3.16.1 REGRESSION]: Simtec Entropy Key (cdc-acm) broken in
 3.16

On Fri, 2014-09-05 at 16:17 +0100, Nix wrote:
> On 5 Sep 2014, Oliver Neukum verbalised:
> 
> > On Fri, 2014-09-05 at 00:40 +0100, Nix wrote:
> >> I'm working around this confusing morass by rebooting into each test
> >> kernel, unplugging and replugging the entropy key if it was fubared,
> >> then rebooting into the same kernel again and seeing if it was still
> >> fubared. But this is not terribly fast, particularly not on a headless
> >> compact-flash-based Geode box which doesn't even complete booting
> >> without the entropy source which this bug cuts off :) so it'll be
> >> sometime tomorrow before I can get this bisection done, I'm afraid.
> >
> > Ugh. My sympathies. I cannot suggest a better method, I am afraid.
> 
> Well, that method doesn't work. I've found pairs of kernels (e.g.
> 59a3d4c3631e553357b7305dc09db1990aa6757c and
> b05d59dfceaea72565b1648af929b037b0f96d7f) where each kernel works on its
> own (rebooting from that kernel into the same kernel keeps a working
> key, so I would normally assume that each kernel is OK) but rebooting
> from the first into the second yields a broken one if it was working
> before (so one of them must, in fact, be broken, but I have no clue
> which one).
> 
> So I can't figure out how to bisect this.
> 
> Any suggestions as to what failure-test I might use, or what other
> methods I might use to figure out what's going wrong? Not knowing
> anything about USB doesn't help here. I don't know for sure that this is
> a cdc-acm problem -- bisecting just the cdc-acm driver was fruitless --
> so it might be something more generally USBish.
> 

Do your kernels work if you start with a known good kernel e.g.
3.15 and then reboot?

	Regards
		Oliver


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