linux-kernel - Re: [PATCH 0/4] thinkpad_acpi: Add support for controlling charge thresholds

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Message-ID: <20131230132619.GA24241@jak-x230>
Date:	Mon, 30 Dec 2013 14:26:19 +0100
From:	Julian Andres Klode <jak@...-linux.org>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	Julian Andres Klode <jak@...-linux.org>,
	Henrique de Moraes Holschuh <ibm-acpi@....eng.br>,
	Matthew Garrett <matthew.garrett@...ula.com>,
	"open list:THINKPAD ACPI EXT..." 
	<ibm-acpi-devel@...ts.sourceforge.net>,
	"open list:THINKPAD ACPI EXT..." 
	<platform-driver-x86@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/4] thinkpad_acpi: Add support for controlling charge
 thresholds

On Sat, Dec 28, 2013 at 08:10:03PM -0200, Henrique de Moraes Holschuh wrote:
> On Sat, 28 Dec 2013, Julian Andres Klode wrote:
> > On Mon, Nov 11, 2013 at 02:56:29PM +0100, Julian Andres Klode wrote:
> > > This patch series adds support for specifying charging thresholds,
> > > forcing a battery to discharge, and inhibiting charging, on ThinkPad
> > > Laptops using Sandy Bridge or newer processors.
> > 
[...]
> > Henrique, it would be really great if you could take a look.
> 
> I did.  I just did not manage to finish looking over it, it is not really
> okay as-is, mostly because it did not create a power-supply device and
> properly extended that thing in a generic way, which would be vastly
> preferable to adding yet another private interface.

Thanks for the response.

I think that a more generic approach is a good idea, but
I don't think creating a new power supply device would be the right
choice because this controls existing supplies rather than being a
supply in itself, and I am not aware of any other kind of power
supply device that allows setting things.

We could extend the existing battery devices and then get paths like
	/sys/class/power_supply/BAT0/start_charge_thresh
which looks `natural'. There is one problem with that approach, though:

A ThinkPad supports multiple batteries: In my case, I could add a slice
battery. But the ACPI driver only exposes a BAT0 device without a slice
being attached (I assume a BAT1 will pop-up if you add a slice battery,
but can't test it, as I don't own one). This means that you can only
configure the slice battery when it's plugged in. I don't know if its
a good idea to work like this.

Another problem is that I don't know any other systems supporting charge
thresholds, and I don't want to dictate interfaces built for ThinkPads
as a generic way. 
-- 
Julian Andres Klode  - Debian Developer, Ubuntu Member

See http://wiki.debian.org/JulianAndresKlode and http://jak-linux.org/.

Please do not top-post if possible.
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