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

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Message-ID: <20141012185845.GB2786@localhost>
Date:	Sun, 12 Oct 2014 20:58:45 +0200
From:	Johan Hovold <johan@...nel.org>
To:	Nix <nix@...eri.org.uk>
Cc:	Paul Martin <pm@...ian.org>, Oliver Neukum <oliver@...kum.org>,
	Johan Hovold <jhovold@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [3.16.1 BISECTED REGRESSION]: Simtec Entropy Key (cdc-acm)
 broken in 3.16

On Sat, Oct 11, 2014 at 11:24:59PM +0100, Nix wrote:
> On 11 Oct 2014, Paul Martin spake thusly:
> 
> > Having been privy to the firmware of the eKey, it is very simplisting,
> > with no implementation whatsoever of any flow control.
> 
> That's what I thought. (Why would something that just provides data at a
> constant rate way below that of even the slowest USB bus *need* flow
> control?)
> 
> One presumes therefore that the kernel suddenly trying to do flow
> control on shutdown would fubar the firmware's internal state, leading
> to the symptoms I see.

The cdc-acm driver was dropping DTR/RTS on shutdown (close) also before
the commit you refer to. One thing it did change however is that this is
now only done if HUPCL is set. Might setting that flag be enough to
prevent the device firmware from crashing?

Johan
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