Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753836Ab2KSQbF (ORCPT ); Mon, 19 Nov 2012 11:31:05 -0500 Received: from iolanthe.rowland.org ([192.131.102.54]:52265 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1753789Ab2KSQbC (ORCPT ); Mon, 19 Nov 2012 11:31:02 -0500 Date: Mon, 19 Nov 2012 11:31:01 -0500 (EST) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Huang Ying cc: Bjorn Helgaas , , , , "Rafael J. Wysocki" , "Rafael J. Wysocki" Subject: Re: [RFC] PCI/PM: Keep runtime PM enabled for unbound PCI devices In-Reply-To: <1353294849-22588-1-git-send-email-ying.huang@intel.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1916 Lines: 41 On Mon, 19 Nov 2012, Huang Ying wrote: > For unbound PCI devices, what we need is: > > - Always in D0 state, because some devices does not work again after > being put into D3 by the PCI bus. > > - In SUSPENDED state if allowed, so that the parent devices can still > be put into low power state. > > To satisfy these requirement, the runtime PM for the unbound PCI > devices are disabled and set to SUSPENDED state. One issue of this > solution is that the PCI devices will be put into SUSPENDED state even > if the SUSPENDED state is forbidden via the sysfs interface > (.../power/control) of the device. This is not an issue for most > devices, because most PCI devices are not used at all if unbounded. > But there are exceptions. For example, unbound VGA card can be used > for display, but suspend its parents make it stop working. > > To fix the issue, we keep the runtime PM enabled when the PCI devices > are unbound. But the runtime PM callbacks will do nothing if the PCI > devices are unbound. This way, we can put the PCI devices into > SUSPENDED state without put the PCI devices into D3 state. > > Known issue: after some changing, pci_dev->driver is used to indicate > whether the PCI devices are bound and whether the runtime PM callbacks > should do nothing. Maybe it is better to use a dedicated flag such as > .skip_rtpm_callbacks. That may improve code readability. I think it's okay like this, especially if you add a comment in pci_runtime_suspend, pci_runtime_resume, and pci_runtime_idle explaining that when pci_dev->driver isn't set, the device should always remain in D0 regardless of the runtime status. Alan Stern -- 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/