From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030236AbWFAQqF (ORCPT ); Thu, 1 Jun 2006 12:46:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030239AbWFAQqF (ORCPT ); Thu, 1 Jun 2006 12:46:05 -0400 Received: from cantor2.suse.de ([195.135.220.15]:26249 "EHLO mx2.suse.de") by vger.kernel.org with ESMTP id S1030236AbWFAQqE (ORCPT ); Thu, 1 Jun 2006 12:46:04 -0400 Date: Thu, 1 Jun 2006 09:43:27 -0700 From: Greg KH To: Alan Stern Cc: Andrew Morton , David Liontooth , linux-kernel@vger.kernel.org, linux-usb-devel@lists.sourceforge.net Subject: Re: [linux-usb-devel] Re: USB devices fail unnecessarily on unpowered hubs Message-ID: <20060601164327.GB29176@kroah.com> References: <20060601030140.172239b0.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 01, 2006 at 10:58:43AM -0400, Alan Stern wrote: > On Thu, 1 Jun 2006, Andrew Morton wrote: > > > 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? > > I'm not sure whether we create a udev event when a new USB device is > connected. Yes we do. It's of the class "usb_device" and you can write a single udev rule to override the power test if you really want to. Of course I don't recommend someone doing this, as it is violating the USB power rules, and it is a good thing that we are finally testing for them. thanks, greg k-h