linux-kernel - Re: [linux-pm] [RFC][PATCH] PM: Introduce new top level suspend and hibernation callbacks (rev. 2)

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Date:	Wed, 26 Mar 2008 15:24:17 +0100
From:	Oliver Neukum <oliver@...kum.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	linux-pm@...ts.linux-foundation.org,
	Alexey Starikovskiy <astarikovskiy@...e.de>,
	Johannes Berg <johannes@...solutions.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [linux-pm] [RFC][PATCH] PM: Introduce new top level suspend	and hibernation callbacks (rev. 2)

Am Mittwoch, 26. März 2008 15:10:01 schrieb Alan Stern:
> > > IMO you must always keep the ordering invariant. If a parent returns an error
> > > the PM core must not wake its children.
> 
> Don't think of it that way.  The PM core doesn't wake anything.  It
> merely notifies drivers that the system sleep is ending, so that the
> drivers can wake their devices.  It's up to the driver to detect
> whether the parent failed to resume, in which case the driver should
> take appropriate action.

How do you propose that every driver should check the power state
of its parent? Without locking the parent?

> The situation is no different from what happens when the user tries to 
> access a mounted USB disk drive after the USB cable has been unplugged.  
> The drivers take care of everything.

That completely throws away the reason to have a PM core. We've made
a guarantee to drivers that they wil not be woken unless their parents are
awake. In fact the semantics of the callbacks are defined in a way that
adding devices to a parent can be enabled. You cannot add children to a
dead parent. It's the very reason for this rewrite.

	Regards
		Oliver
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