Re: [PATCH v4 1/3] gpio: swnode: Add ability to specify native chip selects for SPI

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Tue, Apr 9, 2024 at 3:21 PM Charles Keepax
<ckeepax@xxxxxxxxxxxxxxxxxxxxx> wrote:

> SPI devices can specify a cs-gpios property to enumerate their
> chip selects. Under device tree, a zero entry in this property can
> be used to specify that a particular chip select is using the SPI
> controllers native chip select, for example:
>
>         cs-gpios = <&gpio1 0 0>, <0>;
>
> Here the second chip select is native. However, when using swnodes
> there is currently no way to specify a native chip select. The
> proposal here is to register a swnode_gpio_undefined software node,
> that can be specified to allow the indication of a native chip
> select. For example:
>
> static const struct software_node_ref_args device_cs_refs[] = {
>         {
>                 .node  = &device_gpiochip_swnode,
>                 .nargs = 2,
>                 .args  = { 0, GPIO_ACTIVE_LOW },
>         },
>         {
>                 .node  = &swnode_gpio_undefined,
>                 .nargs = 0,
>         },
> };
>
> Register the swnode as the gpiolib is initialised and
> check in swnode_get_gpio_device if the returned node matches
> swnode_gpio_undefined and return -ENOENT, which matches the behaviour
> of the device tree system when it encounters a 0 phandle.
>
> Signed-off-by: Charles Keepax <ckeepax@xxxxxxxxxxxxxxxxxxxxx>

I love it.
Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx>

Yours,
Linus Walleij