linux-kernel - Re: [RFC][PATCH] PCI / PM: Avoid resuming PCI devices during system suspend

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Message-ID: <2648963.rfs1ehcxce@vostro.rjw.lan>
Date:	Thu, 15 Jan 2015 10:45:05 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Linux PCI <linux-pci@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Aaron Lu <aaron.lu@...el.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [RFC][PATCH] PCI / PM: Avoid resuming PCI devices during system suspend

On Monday, January 12, 2015 11:39:18 AM Alan Stern wrote:
> On Mon, 12 Jan 2015, Rafael J. Wysocki wrote:
> 
> > On Thursday, January 08, 2015 10:51:06 AM Alan Stern wrote:
> > > On Thu, 8 Jan 2015, Rafael J. Wysocki wrote:
> > > 
> > > > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > > 
> > > > Commit f25c0ae2b4c4 (ACPI / PM: Avoid resuming devices in ACPI PM
> > > > domain during system suspend) modified the ACPI PM domain's system
> > > > suspend callbacks to allow devices attached to it to be left in the
> > > > runtime-suspended state during system suspend so as to optimize
> > > > the suspend process.
> > > > 
> > > > This was based on the general mechanism introduced by commit
> > > > aae4518b3124 (PM / sleep: Mechanism to avoid resuming runtime-suspended
> > > > devices unnecessarily).
> > > > 
> > > > Extend that approach to PCI devices by modifying the PCI bus type's
> > > > ->prepare callback to return 1 for devices that are runtime-suspended
> > > > when it is being executed and that are in a suitable power state and
> > > > need not be resumed going forward.
> > > 
> > > Does this correctly handle PCI devices that aren't included in the ACPI
> > > tables?  For example, add-on PCI cards?
> > 
> > Well, it would if it took the case when a device was configured for remote
> > wakeup at run time but was not supposed to wakeup the system from sleep into
> > account.
> > 
> > That needs to be checked in pci_dev_keep_suspended() rather than in the platform
> > callback to cover all devices.
> > 
> > Updated patch follows.
> > 
> > Rafael
> 
> This looks better, thank you.

Well, it still has the problem that the current ACPI wakeup setting may not be
suitable depending on the PM_QOS_FLAG_REMOTE_WAKEUP value which I overlooked
before.

I need to restore the check against adev->wakeup.prepare_count in
acpi_pci_need_resume() to cover that I think.

Will post a v2 with that fixed.


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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