linux-kernel - Re: [PATCH 2/3] pinctrl: ls2k0300: Support Loongson 2K0300 SoC

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Message-ID: <CACRpkdZCs6u6Tyos_ufBoeZ9V+51btEQ2wbPv1GRp5RNGZcUyA@mail.gmail.com>
Date: Thu, 21 Aug 2025 13:27:03 +0200
From: Linus Walleij <linus.walleij@...aro.org>
To: Yao Zi <ziyao@...root.org>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Huacai Chen <chenhuacai@...nel.org>, 
	WANG Xuerui <kernel@...0n.name>, linux-gpio@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, loongarch@...ts.linux.dev, 
	Mingcong Bai <jeffbai@...c.io>, Kexy Biscuit <kexybiscuit@...c.io>
Subject: Re: [PATCH 2/3] pinctrl: ls2k0300: Support Loongson 2K0300 SoC

On Tue, Aug 19, 2025 at 2:41 PM Yao Zi <ziyao@...root.org> wrote:

> > Which is fine if the pins actually cannot be used for GPIO, but if they
> > can, and this is just implicit for unconfigured pins ... then add
> > functions and groups for GPIO.
>
> For 2K0300, we want these pins to be able to multiplexed as GPIOs, but
> since this pinctrl driver could configure nothing for GPIO mode pins, I
> think it's enough to implement only the gpio_request_enable() callback
> and do the multiplexing work here, is this correct?

Yes that is the quick and elegant solution.

> I originally thought it's okay to multiplex pins as GPIO with an usual
> pinctrl configuration, and didn't realize that it causes conflicts on
> strict controllers since the pin will be claimed by both pincontroller
> and GPIO controller. Thanks for the reminder.

This is true as well, some drivers use an explicit "gpio" function
and for these the the new .function_is_gpio() callback is especially
helpful.

I think it is helpful if you're using the callbacks too (we can
determine if we're already in GPIO mode) but it's not necessary.

Yours,
Linus Walleij