linux-kernel - Re: [PATCH v2 3/3] dt-bindings: gpio: Add Nuvoton NPCM750 serial I/O expansion interface(SGPIO)

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Date:   Mon, 14 Nov 2022 11:13:36 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Jim Liu <jim.t90615@...il.com>
Cc:     JJLIU0@...oton.com, KWLIU@...oton.com, brgl@...ev.pl,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, openbmc@...ts.ozlabs.org
Subject: Re: [PATCH v2 3/3] dt-bindings: gpio: Add Nuvoton NPCM750 serial I/O
 expansion interface(SGPIO)

On Mon, Nov 14, 2022 at 9:38 AM Jim Liu <jim.t90615@...il.com> wrote:

> Our sgpio module has 64 pins output and 64 pins input.
> Soc have 8 reg to control 64 output pins
> and  8 reg to control 64 input pins.
> so the pin is only for gpi or gpo.
>
> The common property ngpio can be out or in.
> so i need to create d_out and d_in to control it.
> customers can set the number of output or input pins to use.
> the driver will open the ports to use.
> ex: if  i set d_out=9   and d_in=20
> driver will open two output ports and three input ports.
>
> Another method  is the driver default opens all ports , in this
> situation the driver doesn't need d_out and d_in.

Finally I get it!

Some of the above should go into the binding document so that
others understand it too.

Have you considered splitting this into 2 instances with 2 DT nodes:
one with up to 64 output-only pins and one with up to 64 input-only pins?
That means more nodes in the DT and more compatibles. If all
the registers are in the same place maybe this is not a good
idea.

If you feel you need to keep the two properties, create something custom
for your hardware because this is not generally useful, e.g.

nuvoton,input-ngpios = <...>
nuvoton,output-ngpios = <...>

By this nomenclature it also becomes more evident what is going on.

Yours,
Linus Walleij