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: <175E0F9A9EFCEA46A65F5552BB057298BB5F43F0@bgsmsx502.gar.corp.intel.com>
Date:	Sun, 12 Jul 2009 07:35:07 +0530
From:	"Mahalingam, Nithish" <nithish.mahalingam@...el.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
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)

>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.

Thanks for the reply Rafael. I felt if we are talking about controlling a device clock from a runtime PM framework we should look at extending the Clock framework rather than re-inventing things.

Regards,
Nithish Mahalingam
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