linux-kernel - Re: [RFC][PATCH 2/2] PM: Make system-wide PM and runtime PM handle subsystems consistently

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Date:	Thu, 17 Feb 2011 00:45:48 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Linux-pm mailing list" <linux-pm@...ts.linux-foundation.org>,
	Kevin Hilman <khilman@...com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Greg KH <greg@...ah.com>, LKML <linux-kernel@...r.kernel.org>,
	Magnus Damm <magnus.damm@...il.com>,
	Len Brown <lenb@...nel.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: [RFC][PATCH 2/2] PM: Make system-wide PM and runtime PM handle subsystems consistently

On Wednesday, February 16, 2011, Alan Stern wrote:
> On Wed, 16 Feb 2011, Rafael J. Wysocki wrote:
> 
> > On Wednesday, February 16, 2011, Alan Stern wrote:
> > > On Wed, 16 Feb 2011, Rafael J. Wysocki wrote:
> > > 
> > > > Unfortunately, it doesn't work on my Acer Ferrari One.  The problem is that
> > > > hcd_pci_suspend() fails for the EHCI controller, apparently because the root
> > > > hub is not suspended.  Do root hubs need both class suspend and bus type
> > > > suspend to work at the same time?
> > > 
> > > No, only the bus type suspend method is needed.
> > 
> > Bus type or device type?  It appears to be the latter from reading the code
> > (although admittedly not too thorough).
> 
> You're right.  I forgot about how the PM methods were split up.  :-(
> 
> > > Can you provide the dmesg log using a kernel built with CONFIG_USB_DEBUG?
> > 
> > Well, I know what the problem is.
> > 
> > USB defines usb_device_type pointing to usb_device_pm_ops that provides
> > system-wide PM callbacks only and usb_bus_type pointing to
> > usb_bus_pm_ops that provides runtime PM callbacks only.  So it looks like
> > we should move either the system-wide PM callbacks to usb_bus_pm_ops,
> > or the runtime PM callbacks to usb_device_pm_ops.
> 
> Yes.  IIRC, I did it that way so that the runtime PM routines could be 
> static.  Making them non-static isn't a big deal, though.
> 
> > FWIW, the appended patch helps on my test machine, but I'm not sure if it
> > is the right thing to do.
> 
> It is.  Except that the inline stubs aren't needed for anything; they 
> don't have to be added to usb.h.

OK, I'll remove them, add a changelog and repost.

> > Apart from this I think the order of checks introduced by the $subject patch
> > should be:
> > (1) If dev->class != NULL and dev->class->pm != NULL, use dev->class,
> >     or otherwise
> > (2) if dev->type != NULL and dev->type->pm != NULL, use dev->type,
> >     or otherwise
> > (3) use dev->bus (if present).
> > as that would allow classes and device types to override bus type PM
> > callbacks if they wish to.
> 
> I haven't heard of any device types being present on more than one kind
> of bus, so it makes sense for device types to override bus types.

OK

> But I'm not so sure about the priority we should give to classes.  On the
> other hand, if no classes define a dev_pm_ops then of course it doesn't
> matter.

The change will also affect classes that provide "legacy" suspend-resume
(if there are any, which I'm totally unsure of).

Anyway, I think we need to choose one ordering. :-)

What about type / bus / class , then?

Rafael
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