A charger mode for uboot

[Tuukka.Hastrup@…]

Current power management implications are difficult for users to understand as
we don't hide the underlying hardware details. One part we should do is a
special mode in uboot that can be entered for charging the phone when it's off.

One simple part of this is the logic to not boot a kernel while there would be
too little charge (10%?) in the battery to start and shut down the system
cleanly with still some charge left to get back to uboot. We could simply power
off the phone if there is too little charge, but better usability could be
achieved with a mode that shows the charging progress: whether we are currently
charging and the current battery charge percentage.

In the mode, the user could have a menu with these entries:

1. Fully shut down the phone (going back to 100mA charge?)
2. Toggle: Do/don't boot automatically as soon as there's enough charge
3. Boot now (inactive if not enough charge yet)

If there is some trouble in the charging process or the source disappears, we
should show a warning message. If this continues, the message should be stored
for display at the next boot, and the phone should be fully shut down.

[laforge@…]

1) in a bettery without coulomb counter there is no way to obtain battery charge
percentage
2) if the battery is discharged too much, we cannot even start u-boot but will
have to do 100ma charging until u-boot can be charged
3) solving this properly will require lots of time and lots of measurements, as
well as fixing all current leaks caused by unclean driver shutdown, etc.
otherwise the battery will continue to discharge when the device is powered off
any way.

all in all, I don't really see anyone looking into this issue anytime soon. it
requires all our resources to only get the basics working. anything else is a
nice disctraction for some future time.

[Tuukka.Hastrup@…]

I'm willing to help the project get there sooner, and I'm learning what it
takes. I should've perhaps included from the start a link to a more general
document I'm working on based on my current understanding:
​http://wiki.openmoko.org/wiki/Power_management_requirements

[andy]

Werner did implement this in U-Boot some months ago, for GTA02 anyway, closing as fixed.