From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935795AbXFFVp2 (ORCPT ); Wed, 6 Jun 2007 17:45:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933487AbXFFVpV (ORCPT ); Wed, 6 Jun 2007 17:45:21 -0400 Received: from cassarossa.samfundet.no ([129.241.93.19]:43930 "EHLO cassarossa.samfundet.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756600AbXFFVpU (ORCPT ); Wed, 6 Jun 2007 17:45:20 -0400 X-Greylist: delayed 1471 seconds by postgrey-1.27 at vger.kernel.org; Wed, 06 Jun 2007 17:45:20 EDT Date: Wed, 6 Jun 2007 23:20:46 +0200 From: "Steinar H. Gunderson" To: linux-kernel@vger.kernel.org Subject: USB low-speed bulk transfers Message-ID: <20070606212046.GA16162@uio.no> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Operating-System: Linux 2.6.20.4 on a x86_64 X-Message-Flag: Outlook? --> http://www.mozilla.org/products/thunderbird/ User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org [Please Cc on reply] Hi, I recently bought an USB MIDI interface from ESI (called “ESI MIDI Mate”). It claims to work with Linux, but doesn't -- I've already asked the manufacturer for an explanation, but as I was impatient, I hacked a bit on the drivers to actually make it work... The /proc/bus/usb/devices entry looks like this: T: Bus=04 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 4 Spd=1.5 MxCh= 0 D: Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1 P: Vendor=0a92 ProdID=1001 Rev= 1.04 S: Manufacturer=ESI S: Product=ESI MIDI Mate C:* #Ifs= 2 Cfg#= 1 Atr=80 MxPwr= 20mA I:* If#= 0 Alt= 0 #EPs= 0 Cls=01(audio) Sub=01 Prot=00 Driver=snd-usb-audio I:* If#= 1 Alt= 0 #EPs= 2 Cls=01(audio) Sub=03 Prot=00 Driver=snd-usb-audio E: Ad=81(I) Atr=02(Bulk) MxPS= 4 Ivl=0ms E: Ad=01(O) Atr=02(Bulk) MxPS= 4 Ivl=0ms There are two points worth noting here: - The device is USB low speed. snd-usb-audio simply checks for full/high speed, and refuses any device that isn't. I can hack around this, inverting a few checks etc., and it seems to work reasonably well (probably since the device has no PCM parts). - Both endpoint descriptors are bulk. The HCD driver plain refuses bulk transfers for low-speed; it looks like they are disallowed in the USB standard somehow. If I comment out the check, the driver works (perfectly!), but I guess this isn't acceptable for upstream? Could the check for low-speed bulk transfers be replaced by a kernel warning somehow? I can't see any big harm by allowing them, and obviously, Windows XP and Mac OS X does so. I can supply a patch for the snd-usb-audio specific parts if desired, but I can't guarantee it's the correct fix for cards that support PCM. Not that I know of any PCM-capable low-speed USB sound cards out there... /* Steinar */ -- Homepage: http://www.sesse.net/