From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1754560Ab1HJSGy (ORCPT <rfc822;w@1wt.eu>);
	Wed, 10 Aug 2011 14:06:54 -0400
Received: from cantor2.suse.de ([195.135.220.15]:58298 "EHLO mx2.suse.de"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1754223Ab1HJSGw (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Wed, 10 Aug 2011 14:06:52 -0400
Date: Wed, 10 Aug 2011 20:06:48 +0200
Message-ID: <s5hk4alxhs7.wl%tiwai@suse.de>
From: Takashi Iwai <tiwai@suse.de>
To: Daniel Mack <zonque@gmail.com>
Cc: Alan Stern <stern@rowland.harvard.edu>,
        Florian Mickler <florian@mickler.org>,
        Oliver Neukum <oliver@neukum.org>, linux-usb@vger.kernel.org,
        alsa-devel@alsa-project.org, Clemens Ladisch <clemens@ladisch.de>,
        pedrib@gmail.com, William Light <wrl@illest.net>,
        Greg KH <greg@kroah.com>, linux-kernel@vger.kernel.org,
        Robert Hancock <hancockrwd@gmail.com>
Subject: Re: Allocating buffers for USB transfers (again)
In-Reply-To: <4E42A4AE.4020008@gmail.com>
References: <Pine.LNX.4.44L0.1108101025250.1917-100000@iolanthe.rowland.org>
	<4E42A4AE.4020008@gmail.com>
User-Agent: Wanderlust/2.15.6 (Almost Unreal) SEMI/1.14.6 (Maruoka)
 FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.7 Emacs/23.3
 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO)
MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka")
Content-Type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

At Wed, 10 Aug 2011 17:33:02 +0200,
Daniel Mack wrote:
> 
> On 08/10/2011 04:32 PM, Alan Stern wrote:
> > Looking at the driver's current code, it appears that your patch
> > does not fix the bug properly.  Using discontiguous regions in the
> > transfer buffer is perfectly okay.  The real problem is later on,
> > where you do:
> >
> > if (send_it) { out->number_of_packets = FRAMES_PER_URB;
> >
> > This should be
> >
> > out->number_of_packets = outframe;
> >
> > The way it is now, the USB stack will try to use data from all the
> > frame descriptors, and the last few will be stale because the loop
> > doesn't set them.
> 
> That's actually true, even though it doesn't seem to cause any trouble.
> I tested everything here of course, and the output URBs return back from
> the USB stack with their length fields zeroed out, which then
> causes the stack to send packets with zero-length fields at the end.
> 
> However, doing it right doesn't harm either. Thanks for spotting.
> 
> Takashi, can you apply this version?

Yep, applied now.  Thanks.


Takashi