linux-kernel - RE: sysfs and power management

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Message-ID: <62697B07E9803846BC582181BD6FB6B836EB2994F4@NOK-EUMSG-02.mgdnok.nokia.com>
Date:	Wed, 27 Oct 2010 15:43:49 +0200
From:	<samu.p.onkalo@...ia.com>
To:	<alan@...ux.intel.com>
CC:	<gregkh@...e.de>, <akpm@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>
Subject: RE: sysfs and power management



>-----Original Message-----
>From: ext Alan Cox [mailto:alan@...ux.intel.com]
>
>> I started to wonder if it makes sense to enhance sysfs so that it
>> optionally prodives open / close call backs. Internally sysfs has
>> some bookkeeping about the refcount but this is not visible to the
>> driver. Of course majority of the sysfs users doesn't need that at all
>> and for them this is just overhead.
>
>I think we need it. There doesn't need to be much overhead however as
>there is no need (or sense) in providing per sysfs node open/close
>hooks.

Do you mean per device hook and each sysfs open / close uses 
per device ref-counting.

So the driver would just know that some sysfs  entry is open 
or all the entries are closed. I think that this kind of behavior
is ok for this purpose.

>
>The pm layer also lacks a clean race-free way to actually ascertain
>when the device was last kicked out of pm saving.
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