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

[Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>]

On Tue, Mar 26, 2024 at 02:11:06PM +0000, Charles Keepax 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,
> 	},
> };

I am sorry, I am very late to the party, but wouldn't it all work by
simply setting ".node" to NULL? As far as I can see we have in
software_node_get_reference_args():

	...

	if (index * sizeof(*ref) >= prop->length)
		return -ENOENT;

	ref_array = prop->pointer;
	ref = &ref_array[index];

	refnode = software_node_fwnode(ref->node);
	if (!refnode)
		return -ENOENT;

if ref->node is NULL then software_node_fwnode(ref->node) will return
NULL and we'll get -ENOENT which will bubble up to
gpiod_get_index_optional() in SPI core.

Thanks.

-- 
Dmitry