linux-kernel - Re: [patch update] Re: [linux-pm] Run-time PM idea (was: Re: [RFC][PATCH 0/2] PM: Rearrange core suspend code)

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Date:	Wed, 10 Jun 2009 23:38:34 +0200
From:	Oliver Neukum <oliver@...kum.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	linux-pm@...ts.linux-foundation.org,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch update] Re: [linux-pm] Run-time PM idea (was: Re: [RFC][PATCH 0/2] PM: Rearrange core suspend code)

Am Mittwoch, 10. Juni 2009 21:27:56 schrieb Rafael J. Wysocki:
> > What happens if the parent's parent is also suspended? It seems to me
> > that you must code this recursively.
>
> Hmm, I thought I did.
>
> [Looks]
>
> pm_request_resume(dev) will call pm_request_resume(dev->parent), if
> necessary, and that will call pm_request_resume(dev->parent->parent) and so
> on.  Each of them will queue a work item and the one for the topmost parent
> will be queued first.  So, the resume requests for all parents will be
> executed before the one for the device, due to the fact that the workqueue
> is singlethread.

Sneaky, I overlooked that.

> Well, there is a bug related to it, namely pm_autosuspend() may change the
> status to RPM_SUSPENDED after pm_request_resume() has changed it to
> RPM_WAKE, that needs fixing.

Ok, maybe this is related. You recurse if the parent isn't in RPM_ACTIVE.
But that is not enough. You must ensure that all the nodes higher up stay
in RPM_ACTIVE. It seems to me that you must go up until you find an
active node (or the root) and put it a blocked state.

	Regards
		Oliver

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