From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932592AbWFCHOd (ORCPT ); Sat, 3 Jun 2006 03:14:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932595AbWFCHOd (ORCPT ); Sat, 3 Jun 2006 03:14:33 -0400 Received: from gprs189-60.eurotel.cz ([160.218.189.60]:35857 "EHLO spitz.ucw.cz") by vger.kernel.org with ESMTP id S932592AbWFCHOd (ORCPT ); Sat, 3 Jun 2006 03:14:33 -0400 Date: Tue, 30 May 2006 20:01:35 +0000 From: Pavel Machek To: David Liontooth Cc: linux-kernel@vger.kernel.org, linux-usb-devel@lists.sourceforge.net Subject: Re: USB devices fail unnecessarily on unpowered hubs Message-ID: <20060530200134.GB4074@ucw.cz> References: <447EB0DC.4040203@cogweb.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <447EB0DC.4040203@cogweb.net> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi! > 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." Actually I have exactly opposite problem: my computer (spitz) can't supply full 500mA on its root hub, and linux tries to power up 'hungry' devices, anyway, leading to very weird behaviour. -- Thanks for all the (sleeping) penguins.