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

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Date: Fri, 3 May 2024 10:25:08 +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

Hi Dough,

thanks for your patch!

I'm a bit confused here:

On Wed, Apr 24, 2024 at 8:51 PM Doug Berger <opendmb@...il.com> wrote:


> +               /* Ignore ranges outside of this GPIO chip */
> +               if (pinspec.args[0] >= (chip->offset + chip->ngpio))
> +                       continue;
> +               if (pinspec.args[0] + pinspec.args[2] <= chip->offset)
> +                       continue;

Here pinspec.args[0] and [2] comes directly from the device tree.

The documentation in Documentation/devicetree/bindings/gpio/gpio.txt
says:

> 2.2) Ordinary (numerical) GPIO ranges
> -------------------------------------
>
> It is useful to represent which GPIOs correspond to which pins on which pin
> controllers. The gpio-ranges property described below represents this with
> a discrete set of ranges mapping pins from the pin controller local number space
> to pins in the GPIO controller local number space.
>
> The format is: <[pin controller phandle], [GPIO controller offset],
>                 [pin controller offset], [number of pins]>;
>
> The GPIO controller offset pertains to the GPIO controller node containing the
> range definition.

So I do not understand how pinspec[0] and [2] can ever be compared
to something involving chip->offset which is a Linux-specific offset.

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

I just don't get it.

So NACK until I understand what is going on here.

Yours,
Linus Walleij