From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030239AbWFAQzI (ORCPT ); Thu, 1 Jun 2006 12:55:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030241AbWFAQzI (ORCPT ); Thu, 1 Jun 2006 12:55:08 -0400 Received: from smtp.osdl.org ([65.172.181.4]:9708 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S1030239AbWFAQzG (ORCPT ); Thu, 1 Jun 2006 12:55:06 -0400 Date: Thu, 1 Jun 2006 09:59:13 -0700 From: Andrew Morton To: Alan Stern Cc: liontooth@cogweb.net, linux-kernel@vger.kernel.org, linux-usb-devel@lists.sourceforge.net Subject: Re: USB devices fail unnecessarily on unpowered hubs Message-Id: <20060601095913.06200806.akpm@osdl.org> In-Reply-To: References: <20060601030140.172239b0.akpm@osdl.org> 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, 1 Jun 2006 10:58:43 -0400 (EDT) Alan Stern wrote: > As an alternative, we could allow an "over-budget window" of say 10%. That, plus we should provide a suitable i-know-what-im-doing user override, with the appropriate warnings, as well as a printk which directs users to this option when we decided to disable their device. > Configurations that exceed the power budget by less than that amount would > still be accepted. I don't know whether this would be enough of a help, > however. I've heard of devices that claim to require 200 mA, for > instance. It just doesn't seem right to enable them when the upstream hub > can only provide 100 mA. The power supply spec is a conservative minimum, whereas the device spec is a worst-case maximum. One would expect a lot of devices will work OK when run "out of spec". (Goes away and pats all his 240V plugpacks which are happily working off 110V).