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

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Date:   Tue, 8 Nov 2022 13:59:08 +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)

Hi Jim,

thanks for your patch!

On Tue, Nov 8, 2022 at 10:29 AM Jim Liu <jim.t90615@...il.com> wrote:
>
> NPCM750 include two SGPIO modules.
> Each module supports up to 64 input and 64 output pins.
> the output pin must be serial to parallel device(such as the hc595)
> the input in must be parallel to serial device(such as the hc165)
>
> Signed-off-by: Jim Liu <JJLIU0@...oton.com>
> ---
> Changes for v2:
>    - modify description
(...)

This:

> +  GPIO pins can be programmed to support the following options
> +  - Support interrupt option for each input port and various interrupt
> +    sensitivity option (level-high, level-low, edge-high, edge-low)
> +  - Directly connected to APB bus and its shift clock is from APB bus clock
> +    divided by a programmable value.
> +  - nin_gpios is number of input GPIO lines
> +  - nout_gpios is number of output GPIO lines
> +  - ngpios is number of nin_gpios GPIO lines and nout_gpios GPIO lines.

Why does input/output have to be configured uniquely/static per system?

What is wrong with just using direction_input() and direction_output()
at runtime like everybody else?

> +        nin_gpios = <64>;
> +        nout_gpios = <64>;

Especially since in the example you just set them all to be both input
and output so they all depend on runtime direction configuration
anyway.

Yours,
Linus Walleij