Re: LTC3651 and other GPIO chargers

[Ladislav Michl <ladis@linux-mips.org>]

On Tue, Jun 27, 2017 at 07:39:21AM +0200, Mike Looijmans wrote:
> On 26-06-17 18:21, Ladislav Michl wrote:
> > Hi there!
> > 
> > A driver for LTC3651 was recently added to -next
> > https://patchwork.kernel.org/patch/9717049/
> > which brings a question whenever we want to add separate driver
> > (or vendor specific bindings) for ever growing list of similar
> > chargers. For example those using the same status output lines
> > are: BQ24232HA, LTC4007, LTM8061, RT9502, LT3651, LT3650, TP4056,
> > MAX1737...
> > Others for example BQ24032A and LM3658 (which I have to support)
> > are using different status encoding, ie. LM3658:
> > 
> > stat1	stat2		Condition
> >    0	  0	Power-Down, charging is suspended or interrupted
> >    1	  0	Pre-qualification mode, CC and CV charging
> >    0	  1	Charge is completed
> >    1	  1	Bad battery (Safety timer expired), or LDO mode
> > 
> > What about extending gpio-charger instead?
> > - allow gpio list fdt subnode
> >    - consider each gpio line to represent bit in a word
> > - provide per property subnodes
> >    - each subnode holds a mask and mapping to property values
> > This way we should be able to cover most chargers providing status
> > using gpios. Comments welcome and appreciated - those will turn into
> > implementation.
> 
> It's an interesting idea, and while writing the ltc3651 driver, I was
> thinking along those lines already. However, there are only two gpio charger
> drivers now, so I didn't see the need yet.
> 
> The table is an interesting approach. Something else to consider: Some gpio
> chargers allow control as well, e.g. pulling the "charging" ping low
> externally forces the charging to stop.

Yes, the aforementioned LM3658 chip is one of such chargers. We already
have charger-manager and gpio-regulator, but this doesn't seem to solve
this situation as it provides "software charger ic". So for now I'm
just misusing led class to enable charger - something which indeed needs
to be solved properly.

> Something that might help is to create a "GPIO charger" sub-menu in Kconfig,
> to make hunting for these drivers a bit easier.

I hope number of these driver will stop rising after we have one to rule
them all :-)

Best regards,
	ladis