linux-kernel - Re: [linux-pm] [RFC][PATCH] PM: Introduce core framework for run-time PM of I/O devices (rev. 8)

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Message-Id: <200907111308.44388.rjw@sisk.pl>
Date:	Sat, 11 Jul 2009 13:08:42 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Mahalingam, Nithish" <nithish.mahalingam@...el.com>
Cc:	Magnus Damm <magnus.damm@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Greg KH <gregkh@...e.de>, LKML <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	"Linux-pm mailing list" <linux-pm@...ts.linux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [linux-pm] [RFC][PATCH] PM: Introduce core framework for run-time PM of I/O devices (rev. 8)

On Thursday 09 July 2009, Mahalingam, Nithish wrote:
> Hi,

Hi,

> I am newbee to this mailing list. Please excuse me if I am talking nonsense here.
> 
> 
> 
> On Thu, Jul 9, 2009 at 10:48 PM, Alan Stern<stern@...land.harvard.edu> wrote:
> >> On Thu, 9 Jul 2009, Magnus Damm wrote:
> >>
> >>> Clocks should be stopped as soon as possible without any delay. The
> >>> clock stopping is very cheap performance wise. Also, the clock
> >> stopping is done on bus level without invoking any driver callbacks.
> >>> Delaying the clock stopping does not make any sense to me.
> >>
> >> In that case the device driver or bus subsystem should manage the
> >> device's clock directly.  There's no need to tie it in with the runtime
> >> PM framework.  Simply start the clock before each I/O operation and
> >> stop it afterward.
> 
> > It's not that easy. The clock needs to be enabled to let the hardware
> > device perform device specific stuff. For instance, the clock for the
> > LCD controller needs to be on to redraw the screen. When the driver
> > knows that it's done with the clock it can notify the bus using
> > Runtime PM.
> 
> Is there any plan to look into the "Clock Framework" that was developed as
> part of OMAP and extending this to make it generic for all platforms?

I don't have any plan to do that and I heaven't heard of anyone planning to do
it.

Best,
Rafael
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