linux-kernel - Re: Zaurus suspend saga

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Message-Id: <1252329025.1861.6.camel@hammer.suse.cz>
Date:	Mon, 07 Sep 2009 15:10:25 +0200
From:	Stanislav Brabec <utx@...guin.cz>
To:	Pavel Machek <pavel@....cz>
Cc:	Richard Purdie <rpurdie@...ys.net>, lenz@...wisc.edu,
	kernel list <linux-kernel@...r.kernel.org>,
	Dirk@...er-Online.de, arminlitzel@....de,
	Cyril Hrubis <metan@....cz>, thommycheck@...il.com,
	linux-arm-kernel <linux-arm-kernel@...ts.arm.linux.org.uk>,
	dbaryshkov@...il.com, omegamoon@...il.com, eric.miao@...vell.com,
	Andrea Adami <andrea.adami@...il.com>
Subject: Re: Zaurus suspend saga

Pavel Machek wrote: 
> 
> > Sadly lack of time means I've lost track of the Zaurus kernels but this
> > sounds like all accesses to the SSP buses now go through the SPI layer
> > and when it was converted nobody thought about the impact this would
> > have on the Zaurus charger code.
>
>Unfortunately... Do you have any idea when this conversion took place?

In past, MAX1111 driver was embedded in the Zaurus specific code. Now
MAX1111 is a generic SPI driver and spitz_pm.c calls it.

Maybe it will still work with CONFIG_CORGI_SSP_DEPRECATED.

> > c) We rip the whole thing out and stop supporting "offline" charging.
> 
> How much faster is offline charge, compared to online charging? I have
> impression that online charging basically does not charge anything...

I think that online charging works, but it seems to be slower. I am not
sure, whether it is a hardware or software issue. You can control
charging speed by software, but the final word has the charging chip.

Here are control wires:
SPITZ_SCP_JK_A: output = turns dummy load to 1 kOhm resistor
SPITZ_SCP_JK_B: output = high charging current
SPITZ_SCP_CHRG_ON: output = charging on
SPITZ_SCP_ADC_TEMP_ON: output = turns battery sensor on/off
SPITZ_GPIO_CHRG_FULL input = charging complete
SPITZ_GPIO_AC_IN input = AC adapter is present

MAX1111 inputs:
MAX1111_ACIN_VOLT: Voltage in AC input (after pass of input circuit,
                   before tha final diode)
MAX1111_BATT_TEMP: Battery temperature sensor
MAX1111_BATT_VOLT: Battery voltage

Here are notes from the design:
Pre-charge = 102mA
Fast charge = 680mA
Fast charge set ON = 105mA
Iterm = 55mA

Thresholds:
SPITZ_GPIO_AC_IN:     4.2V (IC charging circuit)
SPITZ_GPIO_FATAL_BAT: 3.0V (voltage detector IC on battery)
PXA270 batt fault:    2.8V (voltage on the main non-regulated power)
CF/SD:                2.8V (voltage required for CF/SD activation, I am
                            not sure, why it is done, because 2.8V is
                            outside of spec anyway)

When I measured my battery, Linux 2.6.26 went to emergency sleep at
3.4V.

Note that battery thresholds probably should not be hardwired in
spitz_pm.c but read from the NAND configuration instead (Andrea Adami
knows, how it can be done).

Here is the datasheet of the charging circuit:
http://www.penguin.cz/~utx/zaurus/datasheets/power/charging/sc801.pdf

There were more problems in the charging code even before:

- The measurement code should work without turning LED on (bootloader
can do it). SPITZ_SCP_JK_A should connect dummy load. I guess it should
be enough for measurement. But comments in the source tree say that is
did not work. I am not sure why.

- It would be nice to have "small travel charger heuristic": Turn fast
charging on, charger "disappears", switch to slow charging, charger
"appears" => stay in slow charging mode, and retry after some time, or
after going to suspend, reset the flag when charger is removed.

- sysfs interface for charging would be nice. For example: Cyril has an
external battery pack and he wants to disable charging of internal
battery from the external battery.

-- 
Best Regards / S pozdravem,

Stanislav Brabec
software developer
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