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

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Date:	Mon, 7 Dec 2009 17:01:15 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Zhang Rui <rui.zhang@...el.com>, "Rafael J. Wysocki" <rjw@...k.pl>,
	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 Mon, 7 Dec 2009, Linus Torvalds wrote:

> On Mon, 7 Dec 2009, Alan Stern wrote:
> > 
> > It only seems that way because you didn't take into account devices 
> > that suspend synchronously but whose children suspend asynchronously.
> 
> But why would I care? If somebody suspends synchronously, then that's what 
> he wants.

It doesn't mean he wants to block unrelated devices from suspending 
asynchronously, merely because they happen to come earlier in the list.

> > A synchronous suspend routine for a device with async child suspends
> > would have to look just like your usb_node_suspend():
> 
> Sure. But that sounds like a "Doctor, it hurts when I do this" situation. 
> Don't do that.
> 
> Make the USB host controller do its suspend asynchronously. We don't 
> suspend PCI bridges anyway, iirc (but I didn't actually check). And at 
> worst, we can make the PCI _bridges_ know about async suspends, and solve 
> it that way - without actually making any normal PCI drivers do it.

This sounds suspiciously like pushing the problem up a level and 
hoping it will go away.  (Sometimes that even works.)

In the end it isn't a very big issue.  Using one vs. two passes in 
dpm_suspend() is pretty unimportant.

Alan Stern

P.S.: In fact I planned all along to handle USB host controllers 
asynchronously anyway, since their resume routines contain some long 
delays.  I was merely using them as an example.

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