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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Date:	Fri, 10 Jul 2009 03:26:45 +0530
From:	"Mahalingam, Nithish" <nithish.mahalingam@...el.com>
To:	Magnus Damm <magnus.damm@...il.com>,
	Alan Stern <stern@...land.harvard.edu>
CC:	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)

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?
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