From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B6954C282CE for ; Wed, 22 May 2019 18:40:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 98C6520881 for ; Wed, 22 May 2019 18:40:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729005AbfEVSj6 (ORCPT ); Wed, 22 May 2019 14:39:58 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:56414 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1728450AbfEVSj5 (ORCPT ); Wed, 22 May 2019 14:39:57 -0400 Received: (qmail 10090 invoked by uid 2102); 22 May 2019 14:39:56 -0400 Received: from localhost (sendmail-bs@127.0.0.1) by localhost with SMTP; 22 May 2019 14:39:56 -0400 Date: Wed, 22 May 2019 14:39:56 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Bjorn Helgaas cc: Kai Heng Feng , Rafael Wysocki , , LKML , Mathias Nyman , Subject: Re: [PATCH] PCI / PM: Don't runtime suspend when device only supports wakeup from D0 In-Reply-To: <20190522181157.GC79339@google.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Wed, 22 May 2019, Bjorn Helgaas wrote: > On Wed, May 22, 2019 at 11:46:25PM +0800, Kai Heng Feng wrote: > > > On May 22, 2019, at 9:48 PM, Bjorn Helgaas wrote: > > > On Wed, May 22, 2019 at 11:42:14AM +0800, Kai Heng Feng wrote: > > >> at 6:23 AM, Bjorn Helgaas wrote: > > >>> On Wed, May 22, 2019 at 12:31:04AM +0800, Kai-Heng Feng wrote: > > >>>> There's an xHC device that doesn't wake when a USB device gets plugged > > >>>> to its USB port. The driver's own runtime suspend callback was called, > > >>>> PME signaling was enabled, but it stays at PCI D0. > > > > ... > > > And I guess this patch basically means we wouldn't call the driver's > > > suspend callback if we're merely going to stay at D0, so the driver > > > would have no idea anything happened. That might match > > > Documentation/power/pci.txt better, because it suggests that the > > > suspend callback is related to putting a device in a low-power state, > > > and D0 is not a low-power state. > > > > Yes, the patch is to let the device stay at D0 and don’t run driver’s own > > runtime suspend routine. > > > > I guess I’ll just proceed to send a V2 with updated commit message? > > Now that I understand what "runtime suspended to D0" means, help me > understand what's actually wrong. Kai's point is that the xhci-hcd driver thinks the device is now in runtime suspend, because the runtime_suspend method has been executed. But in fact the device is still in D0, and as a result, PME signalling may not work correctly. On the other hand, it wasn't clear from the patch description whether this actually causes a problem on real systems. The description only said that the problem was theoretical. > The PCI core apparently *does* enable PME when we "suspend to D0". > But somehow calling the xHCI runtime suspend callback makes the driver > unable to notice when the PME is signaled? According to Kai, PME signalling doesn't work in D0 -- or at least, it is _documented_ not to work in D0 -- even though it is enabled and the device claims to support it. In any case, I don't really see any point in "runtime suspending" a device while leaving it in D0. We might as well just leave it alone. Alan Stern