From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755947Ab0JaOcS (ORCPT ); Sun, 31 Oct 2010 10:32:18 -0400 Received: from cantor2.suse.de ([195.135.220.15]:38253 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755710Ab0JaOcQ (ORCPT ); Sun, 31 Oct 2010 10:32:16 -0400 Date: Sun, 31 Oct 2010 07:25:39 -0700 From: Greg KH To: Onkalo Samu Cc: ext Henrique de Moraes Holschuh , Alan Cox , "alan@linux.intel.com" , "akpm@linux-foundation.org" , "linux-kernel@vger.kernel.org" Subject: Re: sysfs and power management Message-ID: <20101031142539.GA25480@suse.de> References: <1288177143.12206.22.camel@4fid08082> <20101027124816.7087436a@linux.intel.com> <62697B07E9803846BC582181BD6FB6B836EB2994F4@NOK-EUMSG-02.mgdnok.nokia.com> <20101027152809.39701917@lxorguk.ukuu.org.uk> <20101029195039.GA26401@suse.de> <20101030140047.GA24464@khazad-dum.debian.net> <1288526275.2313.14.camel@noppispoppis.nmp.nokia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1288526275.2313.14.camel@noppispoppis.nmp.nokia.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Oct 31, 2010 at 01:57:55PM +0200, Onkalo Samu wrote: > On Sat, 2010-10-30 at 16:00 +0200, ext Henrique de Moraes Holschuh > wrote: > > On Fri, 29 Oct 2010, Greg KH wrote: > > > back to sleep. That's probably the best way to do this, as userspace > > > isn't going to open the sysfs file and not close it instantly anyway > > > after it has read the data (seeking on a sysfs file isn't really > > > recommended, even if it sometimes seems to work.) > > > > Well, it is documented that seek(start of file) on sysfs works, and it > > is ABI already (some userspace uses it on poll/select-capable > > attributes). So, maybe seek(somewhere that is not the start of the > > file) doesn't work -- and it should return an error in that case if it > > doesn't already... but it is a lot more deterministic than "sometimes" > > ;-) > > > > So yes, userspace will open() and not close() a sysfs attribute immediately > > afterwards. It is not only shell crap that interfaces to the kernel over > > sysfs :-) > > > > What I would like to do is: > > Control sensors operating mode and regulators based on the userspace > activity. If no-one is interested about the sensor, it can be turned > totally off including its operating power via regulator framework. > > So far the only accepted interface for the small sensor seems to be > sysfs. I tried use misc device but it was not accepted. Look at the drivers/staging/iio/ subsystem. It is working on a framework that you can use through a character device (I think) to properly manage your drivers in this manner. Try working with those developers as I think it is what you are looking for here. thanks, greg k-h