linux-kernel - Re: [PATCH v4 1/4] dt-bindings: gpio: spacemit: add support for K1 SoC

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Message-ID: <9dc005ef-3cba-4f9d-9d99-6a6fa49d9383@sifive.com>
Date: Tue, 28 Jan 2025 12:50:52 -0600
From: Samuel Holland <samuel.holland@...ive.com>
To: Rob Herring <robh@...nel.org>, Linus Walleij <linus.walleij@...aro.org>
Cc: devicetree@...r.kernel.org, Conor Dooley <conor+dt@...nel.org>,
 Meng Zhang <zhangmeng.kevin@...ux.spacemit.com>, Yixun Lan
 <dlan@...too.org>, linux-gpio@...r.kernel.org,
 Bartosz Golaszewski <brgl@...ev.pl>, linux-kernel@...r.kernel.org,
 Conor Dooley <conor@...nel.org>, Yangyu Chen <cyy@...self.name>,
 Palmer Dabbelt <palmer@...belt.com>, Jesse Taube <mr.bossman075@...il.com>,
 Jisheng Zhang <jszhang@...nel.org>, Paul Walmsley
 <paul.walmsley@...ive.com>, Olof Johansson <olof@...om.net>,
 Inochi Amaoto <inochiama@...look.com>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v4 1/4] dt-bindings: gpio: spacemit: add support for K1
 SoC

On 2025-01-28 10:58 AM, Rob Herring wrote:
> On Tue, Jan 28, 2025 at 10:03 AM Linus Walleij <linus.walleij@...aro.org> wrote:
>>
>> On Tue, Jan 28, 2025 at 4:17 AM Yixun Lan <dlan@...too.org> wrote:
>>
>>> [Rob]
>>>> If Linux can't handle 1 node for N gpio_chip's, then that's a Linux
>>>> problem. Maybe it can, IDK.
>>>
>>> I haven't seen somthing like this to register 1 node for multi gpio_chips..
>>> To gpio/pinctrl maintainer (Linus Walleij), do you have suggestion on this?
>>
>> For Linux we can call bgpio_init() three times and
>> devm_gpiochip_add_data() three times on the result and if we use the
>> approach with three cells (where the second is instance 0,1,2 and the
>> last one the offset 0..31) then it will work all just the same I guess?
>>
>> foo-gpios <&gpio 2 7 GPIO_ACTIVE_LOW>;
>>
>> for offset 7 on block 2 for example.
>>
>> We need a custom xlate function I suppose.
>>
>> It just has not been done that way before, everybody just did
>> 2-cell GPIOs.
> 
> You can do either 3 cells or 2 cells splitting the 1st cell into
> <bank><index>. I'm pretty sure we have some cases of the latter.

There is also at least one example of 3-cell GPIOs:

Documentation/devicetree/bindings/pinctrl/allwinner,sun4i-a10-pinctrl.yaml

It supports controllers with varying numbers of pins per bank and banks in each
instance. Compared to the design described above, it shares a single gpio_chip
across all banks in a controller instance.

Regards,
Samuel