gpio: swnode: Add ability to specify native chip selects for SPI

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.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20240416100904.3738093-2-ckeepax@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>

gpio: swnode: replace gpiochip_find() with gpio_device_find_by_label()

We're porting all users of gpiochip_find() to using gpio_device_find().
Update the swnode GPIO code.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

gpiolib: Clean up headers

There is a few things done:
- include only the headers we are direct user of
- when pointer is in use, provide a forward declaration
- add missing headers
- group generic headers and subsystem headers
- sort each group alphabetically

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

gpiolib: add support for software nodes

Now that static device properties understand notion of child nodes and
references, let's teach gpiolib to handle them:

- GPIOs are represented as a references to software nodes representing
gpiochip
- references must have 2 arguments - GPIO number within the chip and
GPIO flags (GPIO_ACTIVE_LOW/GPIO_ACTIVE_HIGH, etc)
- a new PROPERTY_ENTRY_GPIO() macro is supplied to ensure the above
- name of the software node representing gpiochip must match label of
the gpiochip, as we use it to locate gpiochip structure at runtime

The following illustrates use of software nodes to describe a "System"
button that is currently specified via use of gpio_keys_platform_data
in arch/mips/alchemy/board-mtx1.c. It follows bindings specified in
Documentation/devicetree/bindings/input/gpio-keys.yaml.

static const struct software_node mxt1_gpiochip2_node = {
.name = "alchemy-gpio2",
};

static const struct property_entry mtx1_gpio_button_props[] = {
PROPERTY_ENTRY_U32("linux,code", BTN_0),
PROPERTY_ENTRY_STRING("label", "System button"),
PROPERTY_ENTRY_GPIO("gpios", &mxt1_gpiochip2_node, 7, GPIO_ACTIVE_LOW),
{ }
};

Similarly, arch/arm/mach-tegra/board-paz00.c can be converted to:

static const struct software_node tegra_gpiochip_node = {
.name = "tegra-gpio",
};

static struct property_entry wifi_rfkill_prop[] __initdata = {
PROPERTY_ENTRY_STRING("name", "wifi_rfkill"),
PROPERTY_ENTRY_STRING("type", "wlan"),
PROPERTY_ENTRY_GPIO("reset-gpios",
&tegra_gpiochip_node, 25, GPIO_ACTIVE_HIGH);
PROPERTY_ENTRY_GPIO("shutdown-gpios",
&tegra_gpiochip_node, 85, GPIO_ACTIVE_HIGH);
{ },
};

static struct platform_device wifi_rfkill_device = {
.name = "rfkill_gpio",
.id = -1,
};

...

software_node_register(&tegra_gpiochip_node);
device_create_managed_software_node(&wifi_rfkill_device.dev,
wifi_rfkill_prop, NULL);

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>