Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752279Ab2EXEpy (ORCPT ); Thu, 24 May 2012 00:45:54 -0400 Received: from mail-vc0-f174.google.com ([209.85.220.174]:49900 "EHLO mail-vc0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751335Ab2EXEpm (ORCPT ); Thu, 24 May 2012 00:45:42 -0400 Date: Wed, 23 May 2012 21:45:37 -0700 From: Greg KH To: prasannatsmkumar Cc: linux-kernel@vger.kernel.org Subject: Re: Why USB Link Power Management only for devices connected to root hub Message-ID: <20120524044537.GB14325@kroah.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1168 Lines: 22 On Tue, May 22, 2012 at 11:42:28AM +0530, prasannatsmkumar wrote: > I have started looking into USB stuff. In the EHCI driver code I could > see the comment that "we only support lpm device connected to root hub > yet" in drivers/usb/host/ehci-pci.c line 466 (3.4 kernel - > http://lxr.free-electrons.com/source/drivers/usb/host/ehci-pci.c#L466). > Is there any reason to not support lpm in devices connected to hub > (other than root hub)? Also inside ehci_lpm_check function in > drivers/usb/host/ehci-lpm.c (3.4 kernel - > http://lxr.free-electrons.com/source/drivers/usb/host/ehci-lpm.c) the > USB device is asked to go to LPM mode and there is a wait for 10ms. I > guess the LPM transition (L0 to L1 state transition) should take place > within some micro seconds then why should we wait for 10ms for ACK? Please as USB-specific questions like this on the linux-usb mailing list if you wish to get answers. greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/