linux-kernel - Re: sysfs and power management

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Message-ID: <20101103094452.0cfae4ec@linux.intel.com>
Date:	Wed, 3 Nov 2010 09:44:52 +0000
From:	Alan Cox <alan@...ux.intel.com>
To:	Greg KH <gregkh@...e.de>
Cc:	samu.p.onkalo@...ia.com,
	ext Henrique de Moraes Holschuh <hmh@....eng.br>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: sysfs and power management

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.

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