linux-kernel - Re: [PATCH v3 12/12] ARM: dtsi: axp81x: set pinmux for GPIO0/1 when used as LDOs

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Date:   Wed, 4 Oct 2017 09:35:06 +0200
From:   Quentin Schulz <quentin.schulz@...e-electrons.com>
To:     Chen-Yu Tsai <wens@...e.org>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Lee Jones <lee.jones@...aro.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH v3 12/12] ARM: dtsi: axp81x: set pinmux for GPIO0/1 when
 used as LDOs

Hi Chen-Yu, Linus,

On 03/10/2017 17:08, Chen-Yu Tsai wrote:
> On Tue, Oct 3, 2017 at 10:47 PM, Maxime Ripard
> <maxime.ripard@...e-electrons.com> wrote:
>> Hi Linus,
>>
>> On Tue, Oct 03, 2017 at 09:27:17AM +0000, Linus Walleij wrote:
>>> On Mon, Oct 2, 2017 at 2:08 PM, Quentin Schulz
>>> <quentin.schulz@...e-electrons.com> wrote:
>>>
>>>> On AXP813/818, GPIO0 and GPIO1 can be used as LDO as (respectively)
>>>> ldo_io0 and ldo_io1.
>>> (...)
>>>> +               gpio0_ldo: gpio0_ldo {
>>>> +                       pins = "GPIO0";
>>>> +                       function = "ldo";
>>>> +               };
>>> (...)
>>>> +                       pinctrl-names = "default";
>>>> +                       pinctrl-0 = <&gpio0_ldo>;
>>>>                         /* Disable by default to avoid conflicts with GPIO */
>>>>                         status = "disabled";
>>>
>>> So this is still by default disabled, but you make the default
>>> mode something called "ldo".
>>>
>>> And I think that is to be understood as a low-dropout regulator?
>>>
>>> So is the idea that this should be represented as a regulator
>>> in the end?
>>>
>>> Then I think the state name should not be "default" rather
>>> something like "regulator" and "default" should be the GPIO
>>> mode, as I guess something like that exists.
>>>
>>> Activating a regulator using pin control "default" mode is
>>> not very pretty. It would probably be unintuitive and end
>>> up wasting power because people will get confused about
>>> what is going on.
>>
>> That's not really it. The PMIC has pins that can be muxed either to
>> (regular) GPIOs, an ADC or to an LDO regulator.
>>
>> This is just muxing, the regulator will be enabled and disabled
>> separately through another register. If it wasn't the case, it would
>> indeed be very messy.
> 
> No. Actually they are controlled in the same register, so it is
> very messy. The muxing options are:
> 
>     - 0: drive low
>     - 1: drive high
>     - 2: input with interrupt triggering
>     - 3: LDO on
>     - 4: LDO off
>     - 5~7: floating (or ADC)
> 

Just to be a little more precise,
     - 0: drive low
     - 1: drive high
     - 2: input with interrupt triggering
     - 3: LDO on
     - 4: LDO off
     - 5~7: floating (or ADC)

for AXP813, and
     - 0: drive low
     - 1: drive high
     - 2: input with interrupt triggering
     - 3: LDO on
     - 4: ADC
     - 5~7: floating

for AXP209.

So I think what you suggested Linus is not really relevant here as the
regulator framework will take care of disabling the regulator when
needed (for AXP813 via the ldo_off "muxing" selected by the regulator
framework).

However, there is no LDO off bit for AXP209 and the LDO can't be set to
0V in any other register. What's done now in the regulator driver for
AXP209 is to select the floating "muxing" for the pin when wanting to
disable the regulator. So I guess that's a way to handle it. Should we
do it another way?

Thanks for raising the issue, I frankly haven't thought about that at all.

I have to send a v4 to update the support for AXP813 (basically setting
ADC muxing to 0x5 instead of 0x4, for AXP813) as I misread the muxing
register description when adding support for it.

Thanks,
Quentin
-- 
Quentin Schulz, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com