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SubjectRe: [linux-pm] [RFC][PATCH] PM: Introduce new top level suspend and hibernation callbacks (rev. 2 )
On Tue, 25 Mar 2008, Oliver Neukum wrote:

> Am Dienstag, 25. März 2008 14:06:15 schrieb Rafael J. Wysocki:
> > On Tuesday, 25 of March 2008, Oliver Neukum wrote:
>
> > > A device that cannot wake up is unusable. Shouldn't the pm core disconnect()
> > > such a device?

It's not safe for the PM core to do such things unilaterally. The
decision to unregister a device should be made by the driver or the
subsystem.

(The only problem is that it's impossible to unregister a device from
within its suspend or resume methods. Perhaps there should be a way
for the driver to tell the PM core that the core should unregister the
device as soon as the method returns. I don't know if such a facility
would get used...)

> > Well, if ->resume() returns an error, the driver already knows there's a
> > problem and it can act upon that, at least in principle.
>
> Then why return an error? If a driver returns an error I would assume that
> to indicate an irrecoverable error.

The PM core prints a warning in the system log whenever an error is
returned. There isn't much more it can do.

> > However, the PM core probably shouldn't try to resume the children of a failing
> > device. Also, if ->resume_noirq() fails, it probably is not a good idea to
> > call ->resume() and ->complete() for the same device and for it's children.
>
> Exactly. But we need to define what happens in these cases. If we simply
> ignore the errors, the drivers must be able to deal with IO to half suspended
> devices.

Just so -- it's up to the drivers to deal with this sort of thing. The
PM core can't know the details of what should be done in each case.

For example, if a USB hub can't be resumed then usbcore marks all of
its descendants with USB_STATE_NOTATTACHED. When the children's resume
methods are called, they return without trying to do anything. Later
on khubd takes care of unregistering everything.

Alan Stern

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