linux-kernel - Re: [PATCH v3 3/6] dt-bindings: mfd: da9062: add regulator voltage selection documentation

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Date:   Thu, 12 Dec 2019 16:08:44 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Marco Felsch <m.felsch@...gutronix.de>
Cc:     Adam Thomson <Adam.Thomson.Opensource@...semi.com>,
        Mark Brown <broonie@...nel.org>,
        Support Opensource <Support.Opensource@...semi.com>,
        "lee.jones@...aro.org" <lee.jones@...aro.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "bgolaszewski@...libre.com" <bgolaszewski@...libre.com>,
        "joel@....id.au" <joel@....id.au>,
        "andrew@...id.au" <andrew@...id.au>,
        "lgirdwood@...il.com" <lgirdwood@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>
Subject: Re: [PATCH v3 3/6] dt-bindings: mfd: da9062: add regulator voltage
 selection documentation

On Wed, Dec 11, 2019 at 6:09 PM Marco Felsch <m.felsch@...gutronix.de> wrote:

> I discussed it with a colleague again and he mentioned that pinctrl
> should be named pinctrl instead it should be named padctrl.

Quoting Documentation/driver-api/pinctl.rst:

(...)
Definition of PIN:

- PINS are equal to pads, fingers, balls or whatever packaging input or
  output line you want to control and these are denoted by unsigned integers
  in the range 0..maxpin.
(...)

> We don't
> reconfigure the pad to a other function it is still a device general
> purpose input pad. The hw-signal flow goes always trough the gpio block
> so one argument more for my solution. Also we don't configure the "pad"
> to be a vsel/ena-pin. The hw-pad can only be a gpio or has an alternate
> function (WDKICK for GPIO0, Seq. SYS_EN for GPIO2, Seq. PWR_EN for GPIO4).
> Instead we tell the regulator to use _this_ GPIO e.g. for voltage
> selection so we go the other way around. My last argument why pinctrl
> isn't the correct place is that the GPIO1 can be used for
> regulator-0:vsel-in and for regulator-1:enable-in. So this pad would
> have different states which is invalid IMHO.

Yeah it is just one of these cases where the silicon designer pulled
a line of polysilicone over to the regulator enable signal and put a
switch on it and say "so you can also enable the regulator
with a signal from here", it can be used in parallel with anything
else, which is especially messy.

Special cases require special handling, since the electronic design
of this thing is a bit Rube Goldberg.

Yours,
Linus Walleij