linux-kernel - Re: [patch update] PM: Introduce core framework for run-time PM of I/O devices

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Date:	Sun, 14 Jun 2009 16:18:50 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Oliver Neukum <oliver@...kum.org>,
	Magnus Damm <damm@...l.co.jp>,
	linux-pm@...ts.linux-foundation.org,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>, Greg KH <gregkh@...e.de>
Subject: Re: [patch update] PM: Introduce core framework for run-time PM of
 I/O devices

On Mon, 15 Jun 2009 00:57:31 +0200
"Rafael J. Wysocki" <rjw@...k.pl> wrote:

> On Sunday 14 June 2009, Rafael J. Wysocki wrote:
> > On Sunday 14 June 2009, Rafael J. Wysocki wrote:
> > > Hi,
> > > 
> > > Below is the current version of my "run-time PM for I/O devices"
> > > patch.
> > > 
> > > I've done my best to address the comments received during the
> > > recent discussions, but at the same time I've tried to make the
> > > patch only contain the most essential things.  For this reason,
> > > for example, the sysfs interface is not there and it's going to
> > > be added in a separate patch.
> > > 
> > > Please let me know if you want me to change anything in this
> > > patch or to add anything new to it.  [Magnus, I remember you
> > > wanted something like ->runtime_wakeup() along with
> > > ->runtime_idle(), but I'm not sure it's really necessary.  Please
> > > let me know if you have any particular usage scenario for it.]
> 
> Appended is an update of the patch addressing the today's comments
> from Magnus.

few comments from me

1) For the usecases for upcoming hw from Intel (where you really can't talk to the hw while it's in powersave mode); the locking needs to be
   IRQ safe. Think of it like this:
   Lets assume you get a (shared) interrupt from your device. In the handler you need to make 100% sure that 
    1) you're not suspended at this point .. basically do a forced wakeup right there and then
    2) assure that you're not about to suspend
2) You use jiffies in the API; I would suggest exposing milliseconds instead and internally convert to jiffies;
   milliseconds tends to be a much more natural unit for this sort of thing

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