linux-kernel - Re: [RFD] Automatic suspend

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Message-Id: <200902181605.18363.oliver@neukum.org>
Date:	Wed, 18 Feb 2009 16:05:15 +0100
From:	Oliver Neukum <oliver@...kum.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Pavel Machek <pavel@....cz>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	mark gross <mgross@...ux.intel.com>,
	"Woodruff, Richard" <r-woodruff2@...com>,
	Uli Luckas <u.luckas@...d.de>,
	Igor Stoppa <igor.stoppa@...ia.com>,
	Brian Swetland <swetland@...gle.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [RFD] Automatic suspend

Am Wednesday 18 February 2009 15:51:58 schrieb Arjan van de Ven:
> On Wed, 18 Feb 2009 09:53:48 +0100
> Oliver Neukum <oliver@...kum.org> wrote:
> 
> > Am Wednesday 18 February 2009 00:26:53 schrieb Rafael J. Wysocki:
> > > > Another possibility is to set up independent runtime PM for the
> > > > transport and the device.  This means allowing the possibility
> > > > that the transport is suspended while its child (the device) is
> > > > not.  This is a little simpler (there's only one idle-timeout per
> > > > device, since the link is treated as an independent device), but
> > > > it violates the principle of never suspending a parent while
> > > > there is an active child.
> > > 
> > > Well, I think the first approach would be better.
> > 
> > I am afraid it wouldn't be. How do you deal with shared transports?
> > 
> 
> realistically, something like this you need to design like this
> Step 1) Assume the hardware is smart and can do this for you on the fly,
>         but it might need guidance.
>         (For many busses there are platforms that do this)
> Step 2) For hardware that is not smart, emulate the smartness in the
>         driver, with help of the subsystem. These two together have
>         the right knowledge to make such decisions.

But the transport and the driver may be in different subsystems, e.g.
usb storage.

	Regards
		Oliver


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