linux-kernel - RE: sysfs and power management

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Message-ID: <62697B07E9803846BC582181BD6FB6B836EB55F0AD@NOK-EUMSG-02.mgdnok.nokia.com>
Date:	Wed, 3 Nov 2010 16:00:20 +0100
From:	<samu.p.onkalo@...ia.com>
To:	<gregkh@...e.de>, <alan@...ux.intel.com>
CC:	<hmh@....eng.br>, <alan@...rguk.ukuu.org.uk>,
	<akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>
Subject: RE: sysfs and power management



>-----Original Message-----
>From: ext Greg KH [mailto:gregkh@...e.de]
>Sent: 03 November, 2010 15:09
>To: Alan Cox
>Cc: Onkalo Samu.P (Nokia-MS/Tampere); ext Henrique de Moraes Holschuh;
>Alan Cox; akpm@...ux-foundation.org; linux-kernel@...r.kernel.org
>Subject: Re: sysfs and power management
>
>On Wed, Nov 03, 2010 at 09:44:52AM +0000, Alan Cox wrote:
>> On Mon, 1 Nov 2010 11:07:40 -0700
>> Greg KH <gregkh@...e.de> wrote:
>>
>> > On Mon, Nov 01, 2010 at 04:57:01PM +0000, Alan Cox wrote:
>> > > > I took a look to that. It seems that iio is more or less sysfs
>> > > > based. There are ring buffers and event device which are chardev
>> > > > based but still the data outside ring buffer and the control is
>> > > > sysfs based.
>> > >
>> > > IIO is sysfs dependant, heavyweight and makes no sense for some of
>> > > the sysfs based drivers. IIO is also staging based and Linus
>> > > already threw out the last attempt to unify these drivers sanely
>> > > with an ALS layer - which was smaller, cleaner and better !
>> >
>> > I think we need to revisit this issue again, before iio is merged to
>> > the main kernel tree.  I've been totally ignoring the iio
>user/kernel
>> > api at the moment, waiting for things to settle down there
>>
>> Actually I think there is another way to do it cleanly
>>
>> Keep a flag per device (or per runtime pm struct of device)
>>
>> And on the open/close do
>>
>> 	if (runtime_pm on device && device has SYSFS_PM set)
>> 		pm_runtime_foo
>>
>> so that devices that need to be powered up to handle sysfs requests
>can
>> set a single flag and just work.
>
>That sounds like a reasonable idea.
>

I'm working with the implementation which adds possibility to add per attribute
open_close_notification method with minimal overhead to current system.

-Samu




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