linux-kernel - Re: [PATCH v2 2/2] extcon intel-cht-wc: Enable external charger

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Message-ID: <b7a98801-87fa-ebdd-7142-485c3ec454fb@redhat.com>
Date:   Fri, 22 Feb 2019 10:18:09 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Yauhen Kharuzhy <jekhor@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH v2 2/2] extcon intel-cht-wc: Enable external charger

Hi,

On 20-02-19 22:24, Yauhen Kharuzhy wrote:
> ср, 20 февр. 2019 г. в 18:53, Hans de Goede <hdegoede@...hat.com>:
>>
>> Hi,
>>
>> On 2/19/19 10:24 PM, Yauhen Kharuzhy wrote:
>>> In some configuration external charger "#charge enable" signal is
>>> connected to PMIC. Enable it at device probing to allow charging.
>>>
>>> Save CHGRCTRL0 and CHGDISCTR registers at driver probing and restore
>>> them at driver unbind to re-enable hardware charging control if it was
>>> enabled before.
>>>
>>> Tested at Lenovo Yoga Book (YB1-X91L).

<snip>

>>> @@ -400,6 +487,7 @@ static int cht_wc_extcon_probe(struct platform_device *pdev)
>>>
>>>    disable_sw_control:
>>>        cht_wc_extcon_sw_control(ext, false);
>>> +     cht_wc_restore_initial_state(ext);
>>
>> The restore_initial_state will clober al changes made by the
>> cht_wc_extcon_sw_control call, so we do not need both. Thinking a bit
>> more about this I think it might be best to drop the state save/restore
>> code and just enable hw-control on exit unconditionally. We cannot be
>> sure that te initial state is sane, so just switching to hw-control on
>> exit seem best and requires less code.  Andy, what is your take on this?
> 
> On the other hand we don't know if HW mode is suitable for given
> hardware configuration.
> 
> We can suppose that if existing code with unconditionally switching to
> HW mode didn't cause
> any issues before than we can safely leave this for future discussions
> and add CHGDISCTRL restoring only.

The code would be a lot simpler if we also unconditionally put the chrgdis
pin back in hw control mode, then we only need your modifications to
cht_wc_extcon_sw_control() and we don't need the save / restore state
functions.

On my hardware with a whiskey cove PMIC the firmware comes up with 0x50 in
the CHGDISCTRL register, which means it is under hw control, so we would
normally end up restoring that. I believe your Yoga Book is similar, so
there really is no need for the save / restore state functions.

Regards,

Hans