Comment 1 by Nikolaus Schaller, Apr 18, 2016

Comment 2 by Nikolaus Schaller, Apr 22, 2016

Comment 3 by Nikolaus Schaller, Aug 9, 2016

Comment 4 by Nikolaus Schaller, Nov 15, 2016

There is a code fragment that detects a discrepancy but does not yet 
reprogram the chip as described above:

http://git.goldelico.com/?p=gta04-kernel.git;a=shortlog;h=refs/heads/
work/hns/power/bq27xxx

Comment 5 by Nikolaus Schaller, Jan 8, 2017

writing to the bus needs to extend the access_methods:

http://lxr.free-electrons.com/source/include/linux/power/bq27xxx_batt
ery.h#L32

and platform data (check if we really need this if only i2c devices 
can be re-programmed):

http://lxr.free-electrons.com/source/drivers/w1/slaves/w1_bq27000.c#L
42

we certainly need to add a write_i2c function

http://lxr.free-electrons.com/source/drivers/power/supply/bq27xxx_bat
tery_i2c.c#L36

Comment 6 by Nikolaus Schaller, Jan 13, 2017

Has been added to feature branch:
http://git.goldelico.com/?p=gta04-kernel.git;a=shortlog;h=refs/heads/
work/hns/power/bq27xxx

Unfortunately trying to bring the chip into programming mode fails:

root@letux:~# dmesg|fgrep bq27
[    6.586310] bq27xxx-battery 1-0055: support ver. 1.2.0 enabled
[    6.595440] bq27xxx-battery 1-0055: mismatch in battery capacity: 
1340000 instead of 6000000
[    6.595446] bq27xxx_battery_i2c_write 00 8000 => wr 0x00 0x00 
0x80 [2]
[    6.595836] bq27xxx_battery_i2c_write 00 8000 => wr 0x00 0x00 
0x80 [2]
[    6.596509] bq27xxx_battery_i2c_write 00 0013 => wr 0x00 0x13 
0x00 [2]
[    7.610639] bq27xxx-battery 1-0055: unable to switch to 
programming mode (timeout)
root@letux:~# 

Another thing not implemented is to check for a "battery" 
subnode which defines the battery capacity (and potentially other 
parameters).

Comment 7 by Nikolaus Schaller, Jul 16, 2017

It seems as if a solution arrived upstream in 4.13-rc1:

http://elixir.free-electrons.com/linux/v4.13-rc1/source/include/linux
/power_supply.h#L302

For details and examples how to set up the DT see:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/co
mmit/?id=e2517f3bb44b1ac3772858f4bca0be05d36f492d

So we do no longer need to develop our own driver patches. Just need 
to update the DT.

Comment 8 by Nikolaus Schaller, Jul 18, 2017

First rough test with letux-4.13-rc1 shows:

bq27xxx-battery 1-0055: data memory update not supported for chip

This comes because di->dm_regs == NULL. So something is wrong or 
missing.

Mainly I do not understand how di->dm_regs is intended to be set. 
I have not found any code setting the pointer. Not even in 
linux-next.

Comment 9 by Grazvydas Ignotas, Aug 28, 2017

I've fixed the reprogramming itself, code available here:
https://dev.pyra-handheld.com/notaz/pyra-kernel/commits/pyra-4.10

I can send it as patches, if needed.