linux-kernel - Re: [RFC][PATCH 1/10] PM: Add flag for devices capable of generating run-time wake-up events

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Date:	Mon, 16 Nov 2009 16:00:49 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PCI <linux-pci@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Oliver Neukum <oliver@...kum.org>,
	Shaohua Li <shaohua.li@...el.com>,
	Bjorn Helgaas <bjorn.helgaas@...com>
Subject: Re: [RFC][PATCH 1/10] PM: Add flag for devices capable of generating
 run-time wake-up events

On Mon, 16 Nov 2009, Rafael J. Wysocki wrote:

> On Monday 16 November 2009, Alan Stern wrote:
> > On Mon, 16 Nov 2009, Rafael J. Wysocki wrote:
> > 
> > > From: Rafael J. Wysocki <rjw@...k.pl>
> > > 
> > > Apparently, there are devices that can wake up the system from sleep
> > > states and yet are incapable of generating wake-up events at run
> > > time.  Thus, introduce a flag indicating if given device is capable
> > > of generating run-time wake-up events.
> > 
> > This raises the question: Who is responsible for setting the new 
> > flag?  The code that registers the device?
> 
> Yes, in general.  The platform.

And for non-platform devices (hot-pluggable, for example)?  Presumably 
you would want the driver that detects and registers the device to set 
this flag.

> Actually, I needed it for PCI, but I thought it would be better to put it at
> the core level.
> 
> > What if the kernel can't tell whether or not the device can generate 
> > runtime wake-up events?
> 
> Do you have any specific examples in mind?

What about Matthew's example of an ACPI GPE which might or might not 
cause a runtime wake-up event, depending on the AML code in the BIOS?

> > What if the user wants to override the kernel's setting?  Should there 
> > be a sysfs attribute controlling the flag?
> 
> I have no plans for adding anything like that.

So if the kernel makes a mistake here, the user won't be able to 
correct it.

Alan Stern

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