linux-kernel - Re: [GIT PULL] PM updates for 2.6.33

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Date:	Sat, 5 Dec 2009 16:52:05 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	LKML <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [GIT PULL] PM updates for 2.6.33

On Sun, 6 Dec 2009, Rafael J. Wysocki wrote:
> 
> > It all looks terminally broken: you force async suspend for all PCI 
> > drivers, even when it makes no sense.
> 
> I'm not exactly sure what you're referring to.  The async suspend is not
> forced, it just tells the PM core that it can execute PCI suspend/resume
> callbacks in parallel as long as the devices in question don't depend on each
> other.

That's exactly what I mean by forcing async suspend/resume.

You don't know the ordering rules for PCi devices. Multi-function PCI 
devices commonly share registers - they're on the same chip, after all. 
And even when the _hardware_ is totally independent, we often have 
discovery rules and want to initialize in order because different drivers 
will do things like unregister entirely on suspend, and then re-register 
on resume.

Imagine the mess when two ethernet devices randomly end up coming up with 
different names (eth0/eth1) depending on subtle timing issues.

THAT is why we do things in order. Asynchronous programming is _hard_. 
Just deciding that "all PCI devices can always be resumed and suspended 
asynchronously" is a much MUCH bigger decision than you seem to have 
even realized.

		Linus
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