linux-kernel - Re: Question about userspace-consumer

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Date:	Fri, 14 Aug 2009 18:31:38 +0200
From:	Pavel Machek <pavel@....cz>
To:	Felipe Balbi <me@...ipebalbi.com>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...mlogic.co.uk>,
	Mike Rapoport <mike@...pulab.co.il>,
	linux-kernel@...r.kernel.org
Subject: Re: Question about userspace-consumer

Hi!

> On Mon, Aug 10, 2009 at 10:58:01PM +0100, Mark Brown wrote:
> > On Mon, Aug 10, 2009 at 11:05:54PM +0300, Felipe Balbi wrote:
> > 
> > > I was reading userspace-consumer file ad was wondering whether would be
> > > possible to use that in order to implement what SBS-IF [1] proposes
> > > using sbs-enabled devices.
> > 
> > Looking at that I'm not sure why you wish to push this into user space?
> 
> we need some daemon monitoring battery statuses and taking actions on
> that. Imagine, for example, usb charging where we can:
> 
> a. charge up to 100mA when unconfigured
> b. charge up to 500mA when configured
> c. charge up to 2.5A when with dedicated charger
> d. charge up to 2.5mA when bus is suspended
> 
> handling all of those cases on kernel space seems a little bit odd,
> especially because we still need to take care of state-of-charge,
> pack temperature, time-to-charge, etc etc etc.
> 
> a big looping polling for that stuff in kernel space didn't seem ok to
> me.

As battery charging is done by hw on many common machines... yes it is
okay to do in kernel.

> > Like I say, from a quick read through of the specs I'm not sure that I'd
> > push this into user space but I've not thought about this deeply and may
> > be missing something.
> 
> I think kernel should, as long as possible, only provide functionalities
> for userland to take decisions and actions, no ?
> 
> Handling policy in kernel space I find it a little odd, specially
> because different manufacturers might have different charging algorithms
> they want to implement.

I don't see what policy you see in battery charging. There is
 basically single battery chemistry in use, so this is not as complex
 as you paint it...

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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