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>

drivers/gpio/Makefile

@@ -10,6 +10,7 @@ obj-$(CONFIG_OF_GPIO)		+= gpiolib-of.o
 obj-$(CONFIG_GPIO_CDEV)		+= gpiolib-cdev.o
 obj-$(CONFIG_GPIO_SYSFS)	+= gpiolib-sysfs.o
 obj-$(CONFIG_GPIO_ACPI)		+= gpiolib-acpi.o
+obj-$(CONFIG_GPIOLIB)		+= gpiolib-swnode.o
 
 # Device drivers. Generally keep list sorted alphabetically
 obj-$(CONFIG_GPIO_REGMAP)	+= gpio-regmap.o

drivers/gpio/gpiolib-swnode.c

@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Software Node helpers for the GPIO API
+ *
+ * Copyright 2022 Google LLC
+ */
+#include <linux/err.h>
+#include <linux/errno.h>
+#include <linux/gpio/consumer.h>
+#include <linux/gpio/driver.h>
+#include <linux/kernel.h>
+#include <linux/printk.h>
+#include <linux/property.h>
+#include <linux/string.h>
+
+#include "gpiolib.h"
+#include "gpiolib-swnode.h"
+
+static void swnode_format_propname(const char *con_id, char *propname,
+				   size_t max_size)
+{
+	/*
+	 * Note we do not need to try both -gpios and -gpio suffixes,
+	 * as, unlike OF and ACPI, we can fix software nodes to conform
+	 * to the proper binding.
+	 */
+	if (con_id)
+		snprintf(propname, max_size, "%s-gpios", con_id);
+	else
+		strscpy(propname, "gpios", max_size);
+}
+
+static int swnode_gpiochip_match_name(struct gpio_chip *chip, void *data)
+{
+	return !strcmp(chip->label, data);
+}
+
+static struct gpio_chip *swnode_get_chip(struct fwnode_handle *fwnode)
+{
+	const struct software_node *chip_node;
+	struct gpio_chip *chip;
+
+	chip_node = to_software_node(fwnode);
+	if (!chip_node || !chip_node->name)
+		return ERR_PTR(-EINVAL);
+
+	chip = gpiochip_find((void *)chip_node->name, swnode_gpiochip_match_name);
+	return chip ?: ERR_PTR(-EPROBE_DEFER);
+}
+
+struct gpio_desc *swnode_find_gpio(struct fwnode_handle *fwnode,
+				   const char *con_id, unsigned int idx,
+				   unsigned long *flags)
+{
+	const struct software_node *swnode;
+	struct fwnode_reference_args args;
+	struct gpio_chip *chip;
+	struct gpio_desc *desc;
+	char propname[32]; /* 32 is max size of property name */
+	int error;
+
+	swnode = to_software_node(fwnode);
+	if (!swnode)
+		return ERR_PTR(-EINVAL);
+
+	swnode_format_propname(con_id, propname, sizeof(propname));
+
+	/*
+	 * We expect all swnode-described GPIOs have GPIO number and
+	 * polarity arguments, hence nargs is set to 2.
+	 */
+	error = fwnode_property_get_reference_args(fwnode, propname, NULL, 2, idx, &args);
+	if (error) {
+		pr_debug("%s: can't parse '%s' property of node '%pfwP[%d]'\n",
+			__func__, propname, fwnode, idx);
+		return ERR_PTR(error);
+	}
+
+	chip = swnode_get_chip(args.fwnode);
+	fwnode_handle_put(args.fwnode);
+	if (IS_ERR(chip))
+		return ERR_CAST(chip);
+
+	desc = gpiochip_get_desc(chip, args.args[0]);
+	*flags = args.args[1]; /* We expect native GPIO flags */
+
+	pr_debug("%s: parsed '%s' property of node '%pfwP[%d]' - status (%d)\n",
+		 __func__, propname, fwnode, idx, PTR_ERR_OR_ZERO(desc));
+
+	return desc;
+}
+
+/**
+ * swnode_gpio_count - count the GPIOs associated with a device / function
+ * @fwnode:	firmware node of the GPIO consumer, can be %NULL for
+ *		system-global GPIOs
+ * @con_id:	function within the GPIO consumer
+ *
+ * Return:
+ * The number of GPIOs associated with a device / function or %-ENOENT,
+ * if no GPIO has been assigned to the requested function.
+ */
+int swnode_gpio_count(const struct fwnode_handle *fwnode, const char *con_id)
+{
+	struct fwnode_reference_args args;
+	char propname[32];
+	int count;
+
+	swnode_format_propname(con_id, propname, sizeof(propname));
+
+	/*
+	 * This is not very efficient, but GPIO lists usually have only
+	 * 1 or 2 entries.
+	 */
+	count = 0;
+	while (fwnode_property_get_reference_args(fwnode, propname, NULL, 0,
+						  count, &args) == 0) {
+		fwnode_handle_put(args.fwnode);
+		count++;
+	}
+
+	return count ?: -ENOENT;
+}

drivers/gpio/gpiolib-swnode.h

@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef GPIOLIB_SWNODE_H
+#define GPIOLIB_SWNODE_H
+
+struct fwnode_handle;
+struct gpio_desc;
+
+struct gpio_desc *swnode_find_gpio(struct fwnode_handle *fwnode,
+				   const char *con_id, unsigned int idx,
+				   unsigned long *flags);
+int swnode_gpio_count(const struct fwnode_handle *fwnode, const char *con_id);
+
+#endif /* GPIOLIB_SWNODE_H */

drivers/gpio/gpiolib.c

@@ -26,6 +26,7 @@
 #include "gpiolib.h"
 #include "gpiolib-of.h"
 #include "gpiolib-acpi.h"
+#include "gpiolib-swnode.h"
 #include "gpiolib-cdev.h"
 #include "gpiolib-sysfs.h"
 
@@ -3870,6 +3871,10 @@ static struct gpio_desc *gpiod_find_by_fwnode(struct fwnode_handle *fwnode,
 		dev_dbg(consumer, "using ACPI '%pfw' for '%s' GPIO lookup\n",
 			fwnode, con_id);
 		desc = acpi_find_gpio(fwnode, con_id, idx, flags, lookupflags);
+	} else if (is_software_node(fwnode)) {
+		dev_dbg(consumer, "using swnode '%pfw' for '%s' GPIO lookup\n",
+			fwnode, con_id);
+		desc = swnode_find_gpio(fwnode, con_id, idx, lookupflags);
 	}
 
 	return desc;
@@ -3987,6 +3992,8 @@ int gpiod_count(struct device *dev, const char *con_id)
 		count = of_gpio_get_count(dev, con_id);
 	else if (is_acpi_node(fwnode))
 		count = acpi_gpio_count(dev, con_id);
+	else if (is_software_node(fwnode))
+		count = swnode_gpio_count(fwnode, con_id);
 
 	if (count < 0)
 		count = platform_gpio_count(dev, con_id);

include/linux/gpio/property.h

@@ -0,0 +1,11 @@
+// SPDX-License-Identifier: GPL-2.0+
+#ifndef __LINUX_GPIO_PROPERTY_H
+#define __LINUX_GPIO_PROPERTY_H
+
+#include <dt-bindings/gpio/gpio.h> /* for GPIO_* flags */
+#include <linux/property.h>
+
+#define PROPERTY_ENTRY_GPIO(_name_, _chip_node_, _idx_, _flags_) \
+	PROPERTY_ENTRY_REF(_name_, _chip_node_, _idx_, _flags_)
+
+#endif /* __LINUX_GPIO_PROPERTY_H */