linux-kernel - Re: [PATCH 2/3] gpio: of: support gpio-ranges for multiple gpiochip devices

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Date: Mon, 6 May 2024 09:02:42 +0200
From: Linus Walleij <linus.walleij@...aro.org>
To: Doug Berger <opendmb@...il.com>
Cc: Bartosz Golaszewski <brgl@...ev.pl>, Phil Elwell <phil@...pberrypi.com>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Florian Fainelli <florian.fainelli@...adcom.com>, bcm-kernel-feedback-list@...adcom.com, 
	linux-gpio@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] gpio: of: support gpio-ranges for multiple gpiochip devices

On Fri, May 3, 2024 at 10:21 PM Doug Berger <opendmb@...il.com> wrote:
> On 5/3/2024 1:25 AM, Linus Walleij wrote:

> > It rather looks like you are trying to accomodate the Linux numberspace
> > in the ranges, which it was explicitly designed to avoid.

> The struct gpio_chip documentation in include/linux/gpio/driver.h says:
>
>  > * @offset: when multiple gpio chips belong to the same device this
>  > *    can be used as offset within the device so friendly names can
>  > *    be properly assigned.
>
> It is my understanding that this value represents the offset of a
> gpiochip relative to the GPIO controller device defined by the GPIO
> controller node in device tree. This puts it in the same number space as
> [GPIO controller offset]. I believe it was introduced for the specific
> purpose of translating [GPIO controller offset] values into
> Linux-specific offsets, which is why it is being reused for that purpose
> in this patch.

You're right, I had it confused with .base!

It's because I missed it completely when this new property was added
in 2021.

Sorry for the fuzz.

Yours,
Linus Walleij