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[Libreboot] Battery charging control, Was: Classical (like Phoenix) BIOS

From: Denis 'GNUtoo' Carikli
Subject: [Libreboot] Battery charging control, Was: Classical (like Phoenix) BIOS menu
Date: Thu, 21 Apr 2016 09:39:14 +0200

On Wed, 20 Apr 2016 18:50:30 +0200
Joerg Albert <address@hidden> wrote:
> This depends on the hardware. With Lenovo Thinkpads the i2c (aka
> SMBus) of the battery is connected to the embedded controller only
> (H8S in older models), which also controls charging and is powered as
> soon as the DC power supply is attached.
Indeed, the issue is rather how to access that bus without the
proprietary implementation in the BIOS's SMM.

Practically speaking, I don't even see an easy way to trace what that
SMM code is doing.

Maybe I would need to run the BIOS and dump the SMM code.
I know the SMM region is supposed to be locked, but there are still
many ways to dump it.

Since the LAPIC remapping attack has only been public around 2015 and
that the Lenovo X60 started selling near 2006, it probably works.

> I guess you don't want more control over the battery but over the
> charger, e.g. to implement upper and lower limits for the battery
> charge.
I assumed the battery had a gauge and a charger chip, I'll verify if
that's actually true.


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