linux-kernel - Re: [PATCH] USB: cdc-acm: add quirk for control-line state requests

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Date:	Fri, 07 Nov 2014 11:23:30 +0100
From:	Oliver Neukum <oneukum@...e.de>
To:	Johan Hovold <johan@...nel.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, Nix <nix@...eri.org.uk>,
	Paul Martin <pm@...ian.org>,
	Daniel Silverstone <dsilvers@...ian.org>,
	linux-kernel@...r.kernel.org, stable <stable@...r.kernel.org>
Subject: Re: [PATCH] USB: cdc-acm: add quirk for control-line state requests

On Fri, 2014-11-07 at 10:16 +0100, Johan Hovold wrote:
> On Fri, Nov 07, 2014 at 10:05:12AM +0100, Oliver Neukum wrote:
> > On Thu, 2014-11-06 at 18:08 +0100, Johan Hovold wrote:
> > > Add new quirk for devices that cannot handle control-line state
> > > requests.
> > > 
> > > Note that we currently send these requests to all devices, regardless
> > > of
> > > whether they claim to support it, but that errors are only logged if
> > > support is claimed.
> > 
> > That makes me wonder whether we should do this. What do you think?
> 
> My interpretation was that it's done this way as there may be devices
> with broken CDC headers which fail to set the corresponding capability
> bits, but still support the request (c.f. our recent not-a-modem
> discussion).

Oh well, yes I don't like it, but we can't risk the change.

> In that case, always attempting the request, but only reporting errors
> if support was claimed, makes sense.
> 
> As changing this behaviour now would risk breaking such devices, I
> think black-listing (i.e. this patch) is preferred moving forward.

Unfortunately, yes.

	Regards
		Oliver


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