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Subject: Re: [PATCH 2/2] extcon intel-cht-wc: Enable external charger
To:     Yauhen Kharuzhy <jekhor@gmail.com>
Cc:     linux-kernel@vger.kernel.org,
        MyungJoo Ham <myungjoo.ham@samsung.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>
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From:   Hans de Goede <hdegoede@redhat.com>
Message-ID: <01afde97-544b-423a-c18a-b39410b335ea@redhat.com>
Date:   Thu, 21 Feb 2019 10:33:38 +0100
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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