linux-kernel - modelling power supply / charging logic for ebook reader

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Message-Id: <201102251253.10612.heiko@sntech.de>
Date:	Fri, 25 Feb 2011 12:53:08 +0100
From:	Heiko Stübner <heiko@...ech.de>
To:	linux-kernel@...r.kernel.org
Cc:	Anton Vorontsov <cbou@...l.ru>
Subject: modelling power supply / charging logic for ebook reader

Hi,

Warning newbie questions :-)

I'm trying to implement charging logic for a device. As these are my first 
steps into the kernel I'd like to solicit opinions in which way to proceed.

Hardware: Qisda ebook-reader family - essentially every machine with an epaper 
display from Sipix - build around a s3c2416. Charger IC is a Texas Instruments 
bq24075 connected via gpios. The manufacturers used a fork of 2.6.21.5 and we 
try to make a current kernel usable on the devices.

Somewhere on lkml I read that reimplementing basic charger logic in yet 
another driver is not desired, so I'm looking at using the pda-power driver in 
combination with a simple bq2407x regulator driver based on Philipp Zabels 
driver for the bq24022.

The usb gadget driver has not OTG functionality and vbus detection is done via 
a special gpio. So it seems the gpio-vbus driver seems to be the driver to use 
for this.

Problems:

It's possible to connect the devices usb port to either a normal usb host or a 
dedicated charger with higher current. The charger type is read from 
some usb registers. So my question would be on how to model this with pda-
power.
The ac-part is propably not usable for this as it seems to require a different 
gpio-source. Is implementing some sort of "is_usb_aca"-hook a possible way

The charger also reports its charging status via a gpio. What's the best way 
to implement this with pda-power?
My current idea is to add an is_charging or supply_status hook to pda-power 
and if defined output this value via the get_property method and 
POWER_SUPPLY_STATUS_*.

Or as a complete alternative is it more reasonable to implement a new power-
supply for this and not add more switches to pda-power?
For example the pcf56033-charger driver has exactly this functionality but 
only for a specific device.

As many of the "gadget"-devices only have an usb port but different charging 
sources for it, is it reasonable to build some sort of generic "gadget-power" 
driver analogous to pda-power or does something of this sort exist?

Thanks for any input :-)
Heiko
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