From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lan Tianyu Subject: Re: [RFC PATCH] usb/acpi: Add support usb port power off mechanism for device fixed on the motherboard Date: Sun, 13 May 2012 02:00:57 +0800 Message-ID: <4FAEA559.804@intel.com> References: <4FAD3A51.4010803@intel.com> <20120511181256.GD18754@xanatos> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mga01.intel.com ([192.55.52.88]:60872 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750899Ab2ELSBA (ORCPT ); Sat, 12 May 2012 14:01:00 -0400 In-Reply-To: <20120511181256.GD18754@xanatos> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Sarah Sharp Cc: Alan Stern , lenb@kernel.org, gregkh@linuxfoundation.org, linux-acpi@vger.kernel.org, linux-usb@vger.kernel.org On 2012/5/12 2:12, Sarah Sharp wrote: > On Fri, May 11, 2012 at 01:44:26PM -0400, Alan Stern wrote: >> On Sat, 12 May 2012, Lan Tianyu wrote: >> >>> The power saving depends on devices. I test a usb3.0 ssd. The power saving of >>> power off is about 2.2w more than just selective suspend. In theory, power >>> off can help to save remaining power after selective suspend. >> That's a lot of power! Suspended USB devices aren't supposed to >> consume more than 2.5 mA of bus current, which at 5 V amounts to<= >> 0.0125 W. Does the port really use that much? Or does the SSD have a >> separate power supply that it disables when port power is removed? > I actually suspect that the host controller is powering off several PLLs > if all the ports are powered off. After all, if it doesn't have to pay > attention to connects, disconnects, or remote wakeup, it can power off a > lot more circuitry, and possibly even enter D3cold instead of D3hot when > the PCI device is suspended (depending on what board Tianyu is testing > on). But I agree that it would be interesting to see if the SSD has a > separate power supply that it's turning off. > There is no a separate power supply. All power came from host desktop via usb cable. -- Best Regards Tianyu Lan linux kernel enabling team