From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932132AbWFAJUr (ORCPT ); Thu, 1 Jun 2006 05:20:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932169AbWFAJUr (ORCPT ); Thu, 1 Jun 2006 05:20:47 -0400 Received: from weber.sscnet.ucla.edu ([128.97.42.3]:15502 "EHLO weber.sscnet.ucla.edu") by vger.kernel.org with ESMTP id S932132AbWFAJUq (ORCPT ); Thu, 1 Jun 2006 05:20:46 -0400 Message-ID: <447EB0DC.4040203@cogweb.net> Date: Thu, 01 Jun 2006 02:18:20 -0700 From: David Liontooth User-Agent: Thunderbird 1.5.0.2 (X11/20060517) MIME-Version: 1.0 To: linux-kernel@vger.kernel.org Subject: USB devices fail unnecessarily on unpowered hubs X-Enigmail-Version: 0.94.0.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org 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? David