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

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Date:	Sun, 6 Dec 2009 17:04:47 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Arjan van de Ven <arjan@...radead.org>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"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 Sun, 6 Dec 2009, Arjan van de Ven wrote:

> having spent 30 minutes trying to grok this code, I think there may be
> a trick in using the async function call infrastructure.
> 
> if each USB hub's resume (hub_resume()) would be done as an async
> function call, that would start allowing the hub resumes to go async,
> but this is not enough.
> 
> usb_resume_both() would also then need to be an async call itself, and
> do its "resume the parent" recursion as a async function call, and then
> it needs to do a synchronization before actually resuming the device
> itself (provided it is not a hub or hub like device I suppose).
> 
> the later synchronization guarantees that no device will be resumed
> before it's parent tree structure is resumed, while allowing parallel
> parts of the tree to be resumed in parallel.
> 
> The hard part in this is the locking.... that is getting non-trivial
> once you have multiple asynchronous functions executing.

That's the whole point of Rafael's async suspend/resume framework.  He 
has done the hard work already.

Alan Stern

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