linux-kernel - Re: [RFC 0/5] microchip mpfs/pic64gx pinctrl questions

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Message-ID: <CACRpkdaat_pNJ=_r51JuXXggDtmRrfjmN1AQffJVEA29yoojKg@mail.gmail.com>
Date: Tue, 14 Oct 2025 12:33:36 +0200
From: Linus Walleij <linus.walleij@...aro.org>
To: Conor Dooley <conor@...nel.org>
Cc: Conor Dooley <conor.dooley@...rochip.com>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, linux-kernel@...r.kernel.org, 
	linux-gpio@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [RFC 0/5] microchip mpfs/pic64gx pinctrl questions

On Mon, Oct 13, 2025 at 3:55 PM Conor Dooley <conor@...nel.org> wrote:

[me]
> > entanglement of the GPIO function with another function, then
> > there is the recent patch from Bartosz in commit
> > 11aa02d6a9c222260490f952d041dec6d7f16a92
> > which makes it possible to give the pin control framework
> > an awareness of what a GPIO function is by reading hardware
> > properties, and that it is sometimes separate from other functions.
>
> That is unrelated, but interesting. What I don't really understand from
> the commit message itself is whether this is useful if the pinctrl
> driver is not also acting as a gpiochip driver. In my case, the pinctrl
> hardware is not capable of doing anything more than muxing functions,
> and the gpio function I talk about means routing a "real" gpio
> controller's IO to the pins controlled by the driver I am talking about.
> The 2 in "gpio 2" refers to the specific controller.
> The rest of that thread makes it seem like this is intended for some
> qcom devices where the pinctrl hardware is also a gpiochip.

It's useful if you want to use the .strict setting on the pin
controller and implement the shortcut GPIO enablement functions
such as .gpio_request_enable, .gpio_disable_free
and .gpio_set_direction.

These are often preferred when using the pin control driver
as a "back-end" for a GPIO "front-end".

Yours,
Linus Walleij