From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964868AbWFAJ54 (ORCPT ); Thu, 1 Jun 2006 05:57:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964896AbWFAJ54 (ORCPT ); Thu, 1 Jun 2006 05:57:56 -0400 Received: from smtp.osdl.org ([65.172.181.4]:37322 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S964868AbWFAJ5z (ORCPT ); Thu, 1 Jun 2006 05:57:55 -0400 Date: Thu, 1 Jun 2006 03:01:40 -0700 From: Andrew Morton To: David Liontooth Cc: linux-kernel@vger.kernel.org, linux-usb-devel@lists.sourceforge.net, Alan Stern Subject: Re: USB devices fail unnecessarily on unpowered hubs Message-Id: <20060601030140.172239b0.akpm@osdl.org> In-Reply-To: <447EB0DC.4040203@cogweb.net> References: <447EB0DC.4040203@cogweb.net> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.17; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 01 Jun 2006 02:18:20 -0700 David Liontooth wrote: > Starting with 2.6.16, some USB devices fail unnecessarily on unpowered > hubs. Alan Stern explains, > > "The idea is that the kernel now keeps track of USB power budgets. When a > bus-powered device requires more current than its upstream hub is capable > of providing, the kernel will not configure it. > > Computers' USB ports are capable of providing a full 500 mA, so devices > plugged directly into the computer will work okay. However unpowered hubs > can provide only 100 mA to each port. Some devices require (or claim they > require) more current than that. As a result, they don't get configured > when plugged into an unpowered hub." > > http://www.mail-archive.com/linux-usb-devel@lists.sourceforge.net/msg43480.html > > This is generating a lot of grief and appears to be unnecessarily > strict. Common USB sticks with a MaxPower value just above 100mA, for > instance, typically work fine on unpowered hubs supplying 100mA. > > Is a more user-friendly solution possible? Could the shortfall > information be passed to udev, which would allow rules to be written per > device? > (added linux-usb cc) Yes, it sounds like we're being non-real-worldly here. This change apparently broke things. Did it actually fix anything as well?