Re: [PATCH 2/2] extcon intel-cht-wc: Enable external charger

[Hans de Goede]

Hi,

On 20-02-19 21:28, Yauhen Kharuzhy wrote:
> On Wed, Feb 20, 2019 at 05:42:28PM +0100, Hans de Goede wrote:
> > > > The input-current-limit only specifies how much current the charger may
> > > > draw from the micro-usb for both supplying the laptop as well as for
> > > > charging the battery combined. You can safely set this as high as
> > > > the charger can handle (2A for a dedicated charger).
> > > >
> > > > The BQ25892 should have a *separate* setting for the max current to
> > > > use while charging the battery (assuming that the input current allows
> > > > drawing enough current in the first place). I would hope that those bits
> > > > have some sane value set from the firmware...
> > >
> > > Yes, the charger has separate battery current limit but firmware doesn't
> > > change its default value (2048 mA) while Lenovo's software driver does.
> > > It set battery charging limit to 4 A and input limit to 2 A (it makes
> > > sense because Lenovo adapter and BQ25892 both support voltage increasing
> > > upto 12V).
> >
> > Hmm, I guess your device uses a separate power-barrel charging conector
> > then? 12v over micro-usb requires special negotiation which the Whiskey Cove
> > PMIC does not support AFAIK.
>
> The Yoga Book supports kind of quick charging by negotiate voltage with
> 'current pulse protocol' supported by BQ25892 and Lenovo's wall cube.
> I think that PMIC is not connected to VBUS directly. After charging
> started, BQ25892 driver can ask power adapter to increase voltage
> number of times upto 12V. See
> https://github.com/jekhor/yogabook-linux-kernel/blob/master/drivers/power/supply/bq25890_charger.c#L918
> for example.
>
> > In either case if you want to increase the max battery current to 4A
> > in the kernel, then this will have to be guarded by a DMI check.
>
> Yes.
>
> > I beieve the way to do this wuld be throuh a device-property on the
> > charger which gets set from drivers/i2c/busses/i2c-cht-wc.c, but as
> > said this needs to be behind a DMI check, e cannot just g and boost
> > the max charge current to 4A everywhere.
>
> Yes, I use such method already in the my kernel:
> https://github.com/jekhor/yogabook-linux-kernel/blob/master/drivers/i2c/busses/i2c-cht-wc.c#L247
>
> Anyway, charger tweaking will be next iteration, now I want to complete
> current extcon stuff/

Ok, sounds good.

Regards,

Hans