Immutable branch between the GPIO, ASoC and regulator trees for v6.19-rc1

Add better support for GPIOs shared by multiple consumers.
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Merge tag 'gpio/shared-gpios-for-v6.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/brgl/linux.git into gpio/for-next

Immutable branch between the GPIO, ASoC and regulator trees for v6.19-rc1

Add better support for GPIOs shared by multiple consumers.

arch/arm64/Kconfig.platforms

@@ -316,6 +316,7 @@ config ARCH_QCOM
 	select GPIOLIB
 	select PINCTRL
 	select HAVE_PWRCTRL if PCI
+	select HAVE_SHARED_GPIOS
 	help
 	  This enables support for the ARMv8 based Qualcomm chipsets.
 

drivers/gpio/Kconfig

@@ -6,6 +6,9 @@
 config GPIOLIB_LEGACY
 	def_bool y
 
+config HAVE_SHARED_GPIOS
+	bool
+
 menuconfig GPIOLIB
 	bool "GPIO Support"
 	help
@@ -42,6 +45,11 @@ config GPIOLIB_IRQCHIP
 	select IRQ_DOMAIN
 	bool
 
+config GPIO_SHARED
+	def_bool y
+	depends on HAVE_SHARED_GPIOS || COMPILE_TEST
+	select AUXILIARY_BUS
+
 config DEBUG_GPIO
 	bool "Debug GPIO calls"
 	depends on DEBUG_KERNEL
@@ -2017,6 +2025,15 @@ config GPIO_SIM
 	  This enables the GPIO simulator - a configfs-based GPIO testing
 	  driver.
 
+config GPIO_SHARED_PROXY
+	tristate "Proxy driver for non-exclusive GPIOs"
+	default m
+	depends on GPIO_SHARED || COMPILE_TEST
+	select AUXILIARY_BUS
+	help
+	  This enables the GPIO shared proxy driver - an abstraction layer
+	  for GPIO pins that are shared by multiple devices.
+
 endmenu
 
 menu "GPIO Debugging utilities"

drivers/gpio/Makefile

@@ -12,6 +12,7 @@ obj-$(CONFIG_GPIO_SYSFS)	+= gpiolib-sysfs.o
 obj-$(CONFIG_GPIO_ACPI)		+= gpiolib-acpi.o
 gpiolib-acpi-y			:= gpiolib-acpi-core.o gpiolib-acpi-quirks.o
 obj-$(CONFIG_GPIOLIB)		+= gpiolib-swnode.o
+obj-$(CONFIG_GPIO_SHARED)	+= gpiolib-shared.o
 
 # Device drivers. Generally keep list sorted alphabetically
 obj-$(CONFIG_GPIO_REGMAP)	+= gpio-regmap.o
@@ -160,6 +161,7 @@ obj-$(CONFIG_ARCH_SA1100)		+= gpio-sa1100.o
 obj-$(CONFIG_GPIO_SAMA5D2_PIOBU)	+= gpio-sama5d2-piobu.o
 obj-$(CONFIG_GPIO_SCH311X)		+= gpio-sch311x.o
 obj-$(CONFIG_GPIO_SCH)			+= gpio-sch.o
+obj-$(CONFIG_GPIO_SHARED_PROXY)		+= gpio-shared-proxy.o
 obj-$(CONFIG_GPIO_SIFIVE)		+= gpio-sifive.o
 obj-$(CONFIG_GPIO_SIM)			+= gpio-sim.o
 obj-$(CONFIG_GPIO_SIOX)			+= gpio-siox.o

drivers/gpio/gpio-shared-proxy.c

@@ -0,0 +1,333 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2025 Linaro Ltd.
+ */
+
+#include <linux/auxiliary_bus.h>
+#include <linux/cleanup.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/gpio/consumer.h>
+#include <linux/gpio/driver.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/string_choices.h>
+#include <linux/types.h>
+
+#include "gpiolib-shared.h"
+
+struct gpio_shared_proxy_data {
+	struct gpio_chip gc;
+	struct gpio_shared_desc *shared_desc;
+	struct device *dev;
+	bool voted_high;
+};
+
+static int
+gpio_shared_proxy_set_unlocked(struct gpio_shared_proxy_data *proxy,
+			       int (*set_func)(struct gpio_desc *desc, int value),
+			       int value)
+{
+	struct gpio_shared_desc *shared_desc = proxy->shared_desc;
+	struct gpio_desc *desc = shared_desc->desc;
+	int ret = 0;
+
+	gpio_shared_lockdep_assert(shared_desc);
+
+	if (value) {
+	       /* User wants to set value to high. */
+		if (proxy->voted_high)
+			/* Already voted for high, nothing to do. */
+			goto out;
+
+		/* Haven't voted for high yet. */
+		if (!shared_desc->highcnt) {
+			/*
+			 * Current value is low, need to actually set value
+			 * to high.
+			 */
+			ret = set_func(desc, 1);
+			if (ret)
+				goto out;
+		}
+
+		shared_desc->highcnt++;
+		proxy->voted_high = true;
+
+		goto out;
+	}
+
+	/* Desired value is low. */
+	if (!proxy->voted_high)
+		/* We didn't vote for high, nothing to do. */
+		goto out;
+
+	/* We previously voted for high. */
+	if (shared_desc->highcnt == 1) {
+		/* This is the last remaining vote for high, set value  to low. */
+		ret = set_func(desc, 0);
+		if (ret)
+			goto out;
+	}
+
+	shared_desc->highcnt--;
+	proxy->voted_high = false;
+
+out:
+	if (shared_desc->highcnt)
+		dev_dbg(proxy->dev,
+			"Voted for value '%s', effective value is 'high', number of votes for 'high': %u\n",
+			str_high_low(value), shared_desc->highcnt);
+	else
+		dev_dbg(proxy->dev, "Voted for value 'low', effective value is 'low'\n");
+
+	return ret;
+}
+
+static int gpio_shared_proxy_request(struct gpio_chip *gc, unsigned int offset)
+{
+	struct gpio_shared_proxy_data *proxy = gpiochip_get_data(gc);
+	struct gpio_shared_desc *shared_desc = proxy->shared_desc;
+
+	guard(gpio_shared_desc_lock)(shared_desc);
+
+	proxy->shared_desc->usecnt++;
+
+	dev_dbg(proxy->dev, "Shared GPIO requested, number of users: %u\n",
+		proxy->shared_desc->usecnt);
+
+	return 0;
+}
+
+static void gpio_shared_proxy_free(struct gpio_chip *gc, unsigned int offset)
+{
+	struct gpio_shared_proxy_data *proxy = gpiochip_get_data(gc);
+	struct gpio_shared_desc *shared_desc = proxy->shared_desc;
+
+	guard(gpio_shared_desc_lock)(shared_desc);
+
+	proxy->shared_desc->usecnt--;
+
+	dev_dbg(proxy->dev, "Shared GPIO freed, number of users: %u\n",
+		proxy->shared_desc->usecnt);
+}
+
+static int gpio_shared_proxy_set_config(struct gpio_chip *gc,
+					unsigned int offset, unsigned long cfg)
+{
+	struct gpio_shared_proxy_data *proxy = gpiochip_get_data(gc);
+	struct gpio_shared_desc *shared_desc = proxy->shared_desc;
+	struct gpio_desc *desc = shared_desc->desc;
+	int ret;
+
+	guard(gpio_shared_desc_lock)(shared_desc);
+
+	if (shared_desc->usecnt > 1) {
+		if (shared_desc->cfg != cfg) {
+			dev_dbg(proxy->dev,
+				"Shared GPIO's configuration already set, accepting changes but users may conflict!!\n");
+		} else {
+			dev_dbg(proxy->dev, "Equal config requested, nothing to do\n");
+			return 0;
+		}
+	}
+
+	ret = gpiod_set_config(desc, cfg);
+	if (ret && ret != -ENOTSUPP)
+		return ret;
+
+	shared_desc->cfg = cfg;
+	return 0;
+}
+
+static int gpio_shared_proxy_direction_input(struct gpio_chip *gc,
+					     unsigned int offset)
+{
+	struct gpio_shared_proxy_data *proxy = gpiochip_get_data(gc);
+	struct gpio_shared_desc *shared_desc = proxy->shared_desc;
+	struct gpio_desc *desc = shared_desc->desc;
+	int dir;
+
+	guard(gpio_shared_desc_lock)(shared_desc);
+
+	if (shared_desc->usecnt == 1) {
+		dev_dbg(proxy->dev,
+			"Only one user of this shared GPIO, allowing to set direction to input\n");
+
+		return gpiod_direction_input(desc);
+	}
+
+	dir = gpiod_get_direction(desc);
+	if (dir < 0)
+		return dir;
+
+	if (dir == GPIO_LINE_DIRECTION_OUT) {
+		dev_dbg(proxy->dev,
+			"Shared GPIO's direction already set to output, refusing to change\n");
+		return -EPERM;
+	}
+
+	return 0;
+}
+
+static int gpio_shared_proxy_direction_output(struct gpio_chip *gc,
+					      unsigned int offset, int value)
+{
+	struct gpio_shared_proxy_data *proxy = gpiochip_get_data(gc);
+	struct gpio_shared_desc *shared_desc = proxy->shared_desc;
+	struct gpio_desc *desc = shared_desc->desc;
+	int ret, dir;
+
+	guard(gpio_shared_desc_lock)(shared_desc);
+
+	if (shared_desc->usecnt == 1) {
+		dev_dbg(proxy->dev,
+			"Only one user of this shared GPIO, allowing to set direction to output with value '%s'\n",
+			str_high_low(value));
+
+		ret = gpiod_direction_output(desc, value);
+		if (ret)
+			return ret;
+
+		if (value) {
+			proxy->voted_high = true;
+			shared_desc->highcnt = 1;
+		} else {
+			proxy->voted_high = false;
+			shared_desc->highcnt = 0;
+		}
+
+		return 0;
+	}
+
+	dir = gpiod_get_direction(desc);
+	if (dir < 0)
+		return dir;
+
+	if (dir == GPIO_LINE_DIRECTION_IN) {
+		dev_dbg(proxy->dev,
+			"Shared GPIO's direction already set to input, refusing to change\n");
+		return -EPERM;
+	}
+
+	return gpio_shared_proxy_set_unlocked(proxy, gpiod_direction_output, value);
+}
+
+static int gpio_shared_proxy_get(struct gpio_chip *gc, unsigned int offset)
+{
+	struct gpio_shared_proxy_data *proxy = gpiochip_get_data(gc);
+
+	return gpiod_get_value(proxy->shared_desc->desc);
+}
+
+static int gpio_shared_proxy_get_cansleep(struct gpio_chip *gc,
+					  unsigned int offset)
+{
+	struct gpio_shared_proxy_data *proxy = gpiochip_get_data(gc);
+
+	return gpiod_get_value_cansleep(proxy->shared_desc->desc);
+}
+
+static int gpio_shared_proxy_do_set(struct gpio_shared_proxy_data *proxy,
+				    int (*set_func)(struct gpio_desc *desc, int value),
+				    int value)
+{
+	guard(gpio_shared_desc_lock)(proxy->shared_desc);
+
+	return gpio_shared_proxy_set_unlocked(proxy, set_func, value);
+}
+
+static int gpio_shared_proxy_set(struct gpio_chip *gc, unsigned int offset,
+				 int value)
+{
+	struct gpio_shared_proxy_data *proxy = gpiochip_get_data(gc);
+
+	return gpio_shared_proxy_do_set(proxy, gpiod_set_value, value);
+}
+
+static int gpio_shared_proxy_set_cansleep(struct gpio_chip *gc,
+					  unsigned int offset, int value)
+{
+	struct gpio_shared_proxy_data *proxy = gpiochip_get_data(gc);
+
+	return gpio_shared_proxy_do_set(proxy, gpiod_set_value_cansleep, value);
+}
+
+static int gpio_shared_proxy_get_direction(struct gpio_chip *gc,
+					   unsigned int offset)
+{
+	struct gpio_shared_proxy_data *proxy = gpiochip_get_data(gc);
+
+	return gpiod_get_direction(proxy->shared_desc->desc);
+}
+
+static int gpio_shared_proxy_to_irq(struct gpio_chip *gc, unsigned int offset)
+{
+	struct gpio_shared_proxy_data *proxy = gpiochip_get_data(gc);
+
+	return gpiod_to_irq(proxy->shared_desc->desc);
+}
+
+static int gpio_shared_proxy_probe(struct auxiliary_device *adev,
+				   const struct auxiliary_device_id *id)
+{
+	struct gpio_shared_proxy_data *proxy;
+	struct gpio_shared_desc *shared_desc;
+	struct device *dev = &adev->dev;
+	struct gpio_chip *gc;
+
+	shared_desc = devm_gpiod_shared_get(dev);
+	if (IS_ERR(shared_desc))
+		return PTR_ERR(shared_desc);
+
+	proxy = devm_kzalloc(dev, sizeof(*proxy), GFP_KERNEL);
+	if (!proxy)
+		return -ENOMEM;
+
+	proxy->shared_desc = shared_desc;
+	proxy->dev = dev;
+
+	gc = &proxy->gc;
+	gc->base = -1;
+	gc->ngpio = 1;
+	gc->label = dev_name(dev);
+	gc->parent = dev;
+	gc->owner = THIS_MODULE;
+	gc->can_sleep = shared_desc->can_sleep;
+
+	gc->request = gpio_shared_proxy_request;
+	gc->free = gpio_shared_proxy_free;
+	gc->set_config = gpio_shared_proxy_set_config;
+	gc->direction_input = gpio_shared_proxy_direction_input;
+	gc->direction_output = gpio_shared_proxy_direction_output;
+	if (gc->can_sleep) {
+		gc->set = gpio_shared_proxy_set_cansleep;
+		gc->get = gpio_shared_proxy_get_cansleep;
+	} else {
+		gc->set = gpio_shared_proxy_set;
+		gc->get = gpio_shared_proxy_get;
+	}
+	gc->get_direction = gpio_shared_proxy_get_direction;
+	gc->to_irq = gpio_shared_proxy_to_irq;
+
+	return devm_gpiochip_add_data(dev, &proxy->gc, proxy);
+}
+
+static const struct auxiliary_device_id gpio_shared_proxy_id_table[] = {
+	{ .name = "gpiolib_shared.proxy" },
+	{},
+};
+MODULE_DEVICE_TABLE(auxiliary, gpio_shared_proxy_id_table);
+
+static struct auxiliary_driver gpio_shared_proxy_driver = {
+	.driver = {
+		.name = "gpio-shared-proxy",
+	},
+	.probe = gpio_shared_proxy_probe,
+	.id_table = gpio_shared_proxy_id_table,
+};
+module_auxiliary_driver(gpio_shared_proxy_driver);
+
+MODULE_AUTHOR("Bartosz Golaszewski <bartosz.golaszewski@linaro.org>");
+MODULE_DESCRIPTION("Shared GPIO mux driver.");
+MODULE_LICENSE("GPL");

drivers/gpio/gpiolib-shared.c

@@ -0,0 +1,558 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2025 Linaro Ltd.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/auxiliary_bus.h>
+#include <linux/cleanup.h>
+#include <linux/device.h>
+#include <linux/fwnode.h>
+#include <linux/gpio/consumer.h>
+#include <linux/gpio/machine.h>
+#include <linux/idr.h>
+#include <linux/kref.h>
+#include <linux/list.h>
+#include <linux/lockdep.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/of.h>
+#include <linux/overflow.h>
+#include <linux/printk.h>
+#include <linux/property.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+
+#include "gpiolib.h"
+#include "gpiolib-shared.h"
+
+/* Represents a single reference to a GPIO pin. */
+struct gpio_shared_ref {
+	struct list_head list;
+	/* Firmware node associated with this GPIO's consumer. */
+	struct fwnode_handle *fwnode;
+	/* GPIO flags this consumer uses for the request. */
+	enum gpiod_flags flags;
+	char *con_id;
+	int dev_id;
+	struct auxiliary_device adev;
+	struct gpiod_lookup_table *lookup;
+};
+
+/* Represents a single GPIO pin. */
+struct gpio_shared_entry {
+	struct list_head list;
+	/* Firmware node associated with the GPIO controller. */
+	struct fwnode_handle *fwnode;
+	/* Hardware offset of the GPIO within its chip. */
+	unsigned int offset;
+	/* Index in the property value array. */
+	size_t index;
+	struct gpio_shared_desc *shared_desc;
+	struct kref ref;
+	struct list_head refs;
+};
+
+static LIST_HEAD(gpio_shared_list);
+static DEFINE_MUTEX(gpio_shared_lock);
+static DEFINE_IDA(gpio_shared_ida);
+
+static struct gpio_shared_entry *
+gpio_shared_find_entry(struct fwnode_handle *controller_node,
+		       unsigned int offset)
+{
+	struct gpio_shared_entry *entry;
+
+	list_for_each_entry(entry, &gpio_shared_list, list) {
+		if (entry->fwnode == controller_node && entry->offset == offset)
+			return entry;
+	}
+
+	return NULL;
+}
+
+#if IS_ENABLED(CONFIG_OF)
+static int gpio_shared_of_traverse(struct device_node *curr)
+{
+	struct gpio_shared_entry *entry;
+	size_t con_id_len, suffix_len;
+	struct fwnode_handle *fwnode;
+	struct of_phandle_args args;
+	struct property *prop;
+	unsigned int offset;
+	const char *suffix;
+	int ret, count, i;
+
+	for_each_property_of_node(curr, prop) {
+		/*
+		 * The standard name for a GPIO property is "foo-gpios"
+		 * or "foo-gpio". Some bindings also use "gpios" or "gpio".
+		 * There are some legacy device-trees which have a different
+		 * naming convention and for which we have rename quirks in
+		 * place in gpiolib-of.c. I don't think any of them require
+		 * support for shared GPIOs so for now let's just ignore
+		 * them. We can always just export the quirk list and
+		 * iterate over it here.
+		 */
+		if (!strends(prop->name, "-gpios") &&
+		    !strends(prop->name, "-gpio") &&
+		    strcmp(prop->name, "gpios") != 0 &&
+		    strcmp(prop->name, "gpio") != 0)
+			continue;
+
+		count = of_count_phandle_with_args(curr, prop->name,
+						   "#gpio-cells");
+		if (count <= 0)
+			continue;
+
+		for (i = 0; i < count; i++) {
+			struct device_node *np __free(device_node) = NULL;
+
+			ret = of_parse_phandle_with_args(curr, prop->name,
+							 "#gpio-cells", i,
+							 &args);
+			if (ret)
+				continue;
+
+			np = args.np;
+
+			if (!of_property_present(np, "gpio-controller"))
+				continue;
+
+			/*
+			 * We support 1, 2 and 3 cell GPIO bindings in the
+			 * kernel currently. There's only one old MIPS dts that
+			 * has a one-cell binding but there's no associated
+			 * consumer so it may as well be an error. There don't
+			 * seem to be any 3-cell users of non-exclusive GPIOs,
+			 * so we can skip this as well. Let's occupy ourselves
+			 * with the predominant 2-cell binding with the first
+			 * cell indicating the hardware offset of the GPIO and
+			 * the second defining the GPIO flags of the request.
+			 */
+			if (args.args_count != 2)
+				continue;
+
+			fwnode = of_fwnode_handle(args.np);
+			offset = args.args[0];
+
+			entry = gpio_shared_find_entry(fwnode, offset);
+			if (!entry) {
+				entry = kzalloc(sizeof(*entry), GFP_KERNEL);
+				if (!entry)
+					return -ENOMEM;
+
+				entry->fwnode = fwnode_handle_get(fwnode);
+				entry->offset = offset;
+				entry->index = count;
+				INIT_LIST_HEAD(&entry->refs);
+
+				list_add_tail(&entry->list, &gpio_shared_list);
+			}
+
+			struct gpio_shared_ref *ref __free(kfree) =
+					kzalloc(sizeof(*ref), GFP_KERNEL);
+			if (!ref)
+				return -ENOMEM;
+
+			ref->fwnode = fwnode_handle_get(of_fwnode_handle(curr));
+			ref->flags = args.args[1];
+
+			if (strends(prop->name, "gpios"))
+				suffix = "-gpios";
+			else if (strends(prop->name, "gpio"))
+				suffix = "-gpio";
+			else
+				suffix = NULL;
+			if (!suffix)
+				continue;
+
+			/* We only set con_id if there's actually one. */
+			if (strcmp(prop->name, "gpios") && strcmp(prop->name, "gpio")) {
+				ref->con_id = kstrdup(prop->name, GFP_KERNEL);
+				if (!ref->con_id)
+					return -ENOMEM;
+
+				con_id_len = strlen(ref->con_id);
+				suffix_len = strlen(suffix);
+
+				ref->con_id[con_id_len - suffix_len] = '\0';
+			}
+
+			ref->dev_id = ida_alloc(&gpio_shared_ida, GFP_KERNEL);
+			if (ref->dev_id < 0) {
+				kfree(ref->con_id);
+				return -ENOMEM;
+			}
+
+			if (!list_empty(&entry->refs))
+				pr_debug("GPIO %u at %s is shared by multiple firmware nodes\n",
+					 entry->offset, fwnode_get_name(entry->fwnode));
+
+			list_add_tail(&no_free_ptr(ref)->list, &entry->refs);
+		}
+	}
+
+	for_each_child_of_node_scoped(curr, child) {
+		ret = gpio_shared_of_traverse(child);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static int gpio_shared_of_scan(void)
+{
+	return gpio_shared_of_traverse(of_root);
+}
+#else
+static int gpio_shared_of_scan(void)
+{
+	return 0;
+}
+#endif /* CONFIG_OF */
+
+static void gpio_shared_adev_release(struct device *dev)
+{
+
+}
+
+static int gpio_shared_make_adev(struct gpio_device *gdev,
+				 struct gpio_shared_ref *ref)
+{
+	struct auxiliary_device *adev = &ref->adev;
+	int ret;
+
+	lockdep_assert_held(&gpio_shared_lock);
+
+	memset(adev, 0, sizeof(*adev));
+
+	adev->id = ref->dev_id;
+	adev->name = "proxy";
+	adev->dev.parent = gdev->dev.parent;
+	adev->dev.release = gpio_shared_adev_release;
+
+	ret = auxiliary_device_init(adev);
+	if (ret)
+		return ret;
+
+	ret = auxiliary_device_add(adev);
+	if (ret) {
+		auxiliary_device_uninit(adev);
+		return ret;
+	}
+
+	pr_debug("Created an auxiliary GPIO proxy %s for GPIO device %s\n",
+		 dev_name(&adev->dev), gpio_device_get_label(gdev));
+
+	return 0;
+}
+
+int gpio_shared_add_proxy_lookup(struct device *consumer, unsigned long lflags)
+{
+	const char *dev_id = dev_name(consumer);
+	struct gpio_shared_entry *entry;
+	struct gpio_shared_ref *ref;
+
+	struct gpiod_lookup_table *lookup __free(kfree) =
+			kzalloc(struct_size(lookup, table, 2), GFP_KERNEL);
+	if (!lookup)
+		return -ENOMEM;
+
+	guard(mutex)(&gpio_shared_lock);
+
+	list_for_each_entry(entry, &gpio_shared_list, list) {
+		list_for_each_entry(ref, &entry->refs, list) {
+			if (!device_match_fwnode(consumer, ref->fwnode))
+				continue;
+
+			/* We've already done that on a previous request. */
+			if (ref->lookup)
+				return 0;
+
+			char *key __free(kfree) =
+				kasprintf(GFP_KERNEL,
+					  KBUILD_MODNAME ".proxy.%u",
+					  ref->adev.id);
+			if (!key)
+				return -ENOMEM;
+
+			pr_debug("Adding machine lookup entry for a shared GPIO for consumer %s, with key '%s' and con_id '%s'\n",
+				 dev_id, key, ref->con_id ?: "none");
+
+			lookup->dev_id = dev_id;
+			lookup->table[0] = GPIO_LOOKUP(no_free_ptr(key), 0,
+						       ref->con_id, lflags);
+
+			gpiod_add_lookup_table(no_free_ptr(lookup));
+
+			return 0;
+		}
+	}
+
+	/* We warn here because this can only happen if the programmer borked. */
+	WARN_ON(1);
+	return -ENOENT;
+}
+
+static void gpio_shared_remove_adev(struct auxiliary_device *adev)
+{
+	lockdep_assert_held(&gpio_shared_lock);
+
+	auxiliary_device_uninit(adev);
+	auxiliary_device_delete(adev);
+}
+
+int gpio_device_setup_shared(struct gpio_device *gdev)
+{
+	struct gpio_shared_entry *entry;
+	struct gpio_shared_ref *ref;
+	unsigned long *flags;
+	int ret;
+
+	guard(mutex)(&gpio_shared_lock);
+
+	list_for_each_entry(entry, &gpio_shared_list, list) {
+		list_for_each_entry(ref, &entry->refs, list) {
+			if (gdev->dev.parent == &ref->adev.dev) {
+				/*
+				 * This is a shared GPIO proxy. Mark its
+				 * descriptor as such and return here.
+				 */
+				__set_bit(GPIOD_FLAG_SHARED_PROXY,
+					  &gdev->descs[0].flags);
+				return 0;
+			}
+		}
+	}
+
+	/*
+	 * This is not a shared GPIO proxy but it still may be the device
+	 * exposing shared pins. Find them and create the proxy devices.
+	 */
+	list_for_each_entry(entry, &gpio_shared_list, list) {
+		if (!device_match_fwnode(&gdev->dev, entry->fwnode))
+			continue;
+
+		if (list_count_nodes(&entry->refs) <= 1)
+			continue;
+
+		flags = &gdev->descs[entry->offset].flags;
+
+		__set_bit(GPIOD_FLAG_SHARED, flags);
+		/*
+		 * Shared GPIOs are not requested via the normal path. Make
+		 * them inaccessible to anyone even before we register the
+		 * chip.
+		 */
+		__set_bit(GPIOD_FLAG_REQUESTED, flags);
+
+		pr_debug("GPIO %u owned by %s is shared by multiple consumers\n",
+			 entry->offset, gpio_device_get_label(gdev));
+
+		list_for_each_entry(ref, &entry->refs, list) {
+			pr_debug("Setting up a shared GPIO entry for %s\n",
+				 fwnode_get_name(ref->fwnode));
+
+			ret = gpio_shared_make_adev(gdev, ref);
+			if (ret)
+				return ret;
+		}
+	}
+
+	return 0;
+}
+
+void gpio_device_teardown_shared(struct gpio_device *gdev)
+{
+	struct gpio_shared_entry *entry;
+	struct gpio_shared_ref *ref;
+
+	guard(mutex)(&gpio_shared_lock);
+
+	list_for_each_entry(entry, &gpio_shared_list, list) {
+		if (!device_match_fwnode(&gdev->dev, entry->fwnode))
+			continue;
+
+		list_for_each_entry(ref, &entry->refs, list) {
+			gpiod_remove_lookup_table(ref->lookup);
+			kfree(ref->lookup->table[0].key);
+			kfree(ref->lookup);
+			ref->lookup = NULL;
+			gpio_shared_remove_adev(&ref->adev);
+		}
+	}
+}
+
+static void gpio_shared_release(struct kref *kref)
+{
+	struct gpio_shared_entry *entry =
+		container_of(kref, struct gpio_shared_entry, ref);
+	struct gpio_shared_desc *shared_desc = entry->shared_desc;
+
+	guard(mutex)(&gpio_shared_lock);
+
+	gpio_device_put(shared_desc->desc->gdev);
+	if (shared_desc->can_sleep)
+		mutex_destroy(&shared_desc->mutex);
+	kfree(shared_desc);
+	entry->shared_desc = NULL;
+}
+
+static void gpiod_shared_put(void *data)
+{
+	struct gpio_shared_entry *entry = data;
+
+	lockdep_assert_not_held(&gpio_shared_lock);
+
+	kref_put(&entry->ref, gpio_shared_release);
+}
+
+static struct gpio_shared_desc *
+gpiod_shared_desc_create(struct gpio_shared_entry *entry)
+{
+	struct gpio_shared_desc *shared_desc;
+	struct gpio_device *gdev;
+
+	shared_desc = kzalloc(sizeof(*shared_desc), GFP_KERNEL);
+	if (!shared_desc)
+		return ERR_PTR(-ENOMEM);
+
+	gdev = gpio_device_find_by_fwnode(entry->fwnode);
+	if (!gdev) {
+		kfree(shared_desc);
+		return ERR_PTR(-EPROBE_DEFER);
+	}
+
+	shared_desc->desc = &gdev->descs[entry->offset];
+	shared_desc->can_sleep = gpiod_cansleep(shared_desc->desc);
+	if (shared_desc->can_sleep)
+		mutex_init(&shared_desc->mutex);
+	else
+		spin_lock_init(&shared_desc->spinlock);
+
+	return shared_desc;
+}
+
+static struct gpio_shared_entry *gpiod_shared_find(struct auxiliary_device *adev)
+{
+	struct gpio_shared_desc *shared_desc;
+	struct gpio_shared_entry *entry;
+	struct gpio_shared_ref *ref;
+
+	guard(mutex)(&gpio_shared_lock);
+
+	list_for_each_entry(entry, &gpio_shared_list, list) {
+		list_for_each_entry(ref, &entry->refs, list) {
+			if (adev != &ref->adev)
+				continue;
+
+			if (entry->shared_desc) {
+				kref_get(&entry->ref);
+				return entry;
+			}
+
+			shared_desc = gpiod_shared_desc_create(entry);
+			if (IS_ERR(shared_desc))
+				return ERR_CAST(shared_desc);
+
+			kref_init(&entry->ref);
+			entry->shared_desc = shared_desc;
+
+			pr_debug("Device %s acquired a reference to the shared GPIO %u owned by %s\n",
+				 dev_name(&adev->dev), gpiod_hwgpio(shared_desc->desc),
+				 gpio_device_get_label(shared_desc->desc->gdev));
+
+
+			return entry;
+		}
+	}
+
+	return ERR_PTR(-ENOENT);
+}
+
+struct gpio_shared_desc *devm_gpiod_shared_get(struct device *dev)
+{
+	struct gpio_shared_entry *entry;
+	int ret;
+
+	entry = gpiod_shared_find(to_auxiliary_dev(dev));
+	if (IS_ERR(entry))
+		return ERR_CAST(entry);
+
+	ret = devm_add_action_or_reset(dev, gpiod_shared_put, entry);
+	if (ret)
+		return ERR_PTR(ret);
+
+	return entry->shared_desc;
+}
+EXPORT_SYMBOL_GPL(devm_gpiod_shared_get);
+
+static void gpio_shared_drop_ref(struct gpio_shared_ref *ref)
+{
+	list_del(&ref->list);
+	kfree(ref->con_id);
+	ida_free(&gpio_shared_ida, ref->dev_id);
+	fwnode_handle_put(ref->fwnode);
+	kfree(ref);
+}
+
+static void gpio_shared_drop_entry(struct gpio_shared_entry *entry)
+{
+	list_del(&entry->list);
+	fwnode_handle_put(entry->fwnode);
+	kfree(entry);
+}
+
+/*
+ * This is only called if gpio_shared_init() fails so it's in fact __init and
+ * not __exit.
+ */
+static void __init gpio_shared_teardown(void)
+{
+	struct gpio_shared_entry *entry, *epos;
+	struct gpio_shared_ref *ref, *rpos;
+
+	list_for_each_entry_safe(entry, epos, &gpio_shared_list, list) {
+		list_for_each_entry_safe(ref, rpos, &entry->refs, list)
+			gpio_shared_drop_ref(ref);
+
+		gpio_shared_drop_entry(entry);
+	}
+}
+
+static void gpio_shared_free_exclusive(void)
+{
+	struct gpio_shared_entry *entry, *epos;
+
+	list_for_each_entry_safe(entry, epos, &gpio_shared_list, list) {
+		if (list_count_nodes(&entry->refs) > 1)
+			continue;
+
+		gpio_shared_drop_ref(list_first_entry(&entry->refs,
+						      struct gpio_shared_ref,
+						      list));
+		gpio_shared_drop_entry(entry);
+	}
+}
+
+static int __init gpio_shared_init(void)
+{
+	int ret;
+
+	/* Right now, we only support OF-based systems. */
+	ret = gpio_shared_of_scan();
+	if (ret) {
+		gpio_shared_teardown();
+		pr_err("Failed to scan OF nodes for shared GPIOs: %d\n", ret);
+		return ret;
+	}
+
+	gpio_shared_free_exclusive();
+
+	pr_debug("Finished scanning firmware nodes for shared GPIOs\n");
+	return 0;
+}
+postcore_initcall(gpio_shared_init);

drivers/gpio/gpiolib-shared.h

@@ -0,0 +1,71 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __LINUX_GPIO_SHARED_H
+#define __LINUX_GPIO_SHARED_H
+
+#include <linux/cleanup.h>
+#include <linux/lockdep.h>
+#include <linux/mutex.h>
+#include <linux/spinlock.h>
+
+struct gpio_device;
+struct gpio_desc;
+struct device;
+
+#if IS_ENABLED(CONFIG_GPIO_SHARED)
+
+int gpio_device_setup_shared(struct gpio_device *gdev);
+void gpio_device_teardown_shared(struct gpio_device *gdev);
+int gpio_shared_add_proxy_lookup(struct device *consumer, unsigned long lflags);
+
+#else
+
+static inline int gpio_device_setup_shared(struct gpio_device *gdev)
+{
+	return 0;
+}
+
+static inline void gpio_device_teardown_shared(struct gpio_device *gdev) { }
+
+static inline int gpio_shared_add_proxy_lookup(struct device *consumer,
+					       unsigned long lflags)
+{
+	return 0;
+}
+
+#endif /* CONFIG_GPIO_SHARED */
+
+struct gpio_shared_desc {
+	struct gpio_desc *desc;
+	bool can_sleep;
+	unsigned long cfg;
+	unsigned int usecnt;
+	unsigned int highcnt;
+	union {
+		struct mutex mutex;
+		spinlock_t spinlock;
+	};
+};
+
+struct gpio_shared_desc *devm_gpiod_shared_get(struct device *dev);
+
+DEFINE_LOCK_GUARD_1(gpio_shared_desc_lock, struct gpio_shared_desc,
+	if (_T->lock->can_sleep)
+		mutex_lock(&_T->lock->mutex);
+	else
+		spin_lock_irqsave(&_T->lock->spinlock, _T->flags),
+	if (_T->lock->can_sleep)
+		mutex_unlock(&_T->lock->mutex);
+	else
+		spin_unlock_irqrestore(&_T->lock->spinlock, _T->flags),
+	unsigned long flags)
+
+static inline void gpio_shared_lockdep_assert(struct gpio_shared_desc *shared_desc)
+{
+	if (shared_desc->can_sleep)
+		lockdep_assert_held(&shared_desc->mutex);
+	else
+		lockdep_assert_held(&shared_desc->spinlock);
+}
+
+#endif /* __LINUX_GPIO_SHARED_H */

drivers/gpio/gpiolib.c

@@ -37,6 +37,7 @@
 #include "gpiolib-acpi.h"
 #include "gpiolib-cdev.h"
 #include "gpiolib-of.h"
+#include "gpiolib-shared.h"
 #include "gpiolib-swnode.h"
 #include "gpiolib-sysfs.h"
 #include "gpiolib.h"
@@ -1213,6 +1214,10 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 	if (ret)
 		goto err_remove_irqchip_mask;
 
+	ret = gpio_device_setup_shared(gdev);
+	if (ret)
+		goto err_remove_irqchip;
+
 	/*
 	 * By first adding the chardev, and then adding the device,
 	 * we get a device node entry in sysfs under
@@ -1224,10 +1229,13 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 	if (gpiolib_initialized) {
 		ret = gpiochip_setup_dev(gdev);
 		if (ret)
-			goto err_remove_irqchip;
+			goto err_teardown_shared;
 	}
+
 	return 0;
 
+err_teardown_shared:
+	gpio_device_teardown_shared(gdev);
 err_remove_irqchip:
 	gpiochip_irqchip_remove(gc);
 err_remove_irqchip_mask:
@@ -1296,6 +1304,7 @@ void gpiochip_remove(struct gpio_chip *gc)
 	/* Numb the device, cancelling all outstanding operations */
 	rcu_assign_pointer(gdev->chip, NULL);
 	synchronize_srcu(&gdev->srcu);
+	gpio_device_teardown_shared(gdev);
 	gpiochip_irqchip_remove(gc);
 	acpi_gpiochip_remove(gc);
 	of_gpiochip_remove(gc);
@@ -3988,6 +3997,26 @@ int gpiod_set_consumer_name(struct gpio_desc *desc, const char *name)
 }
 EXPORT_SYMBOL_GPL(gpiod_set_consumer_name);
 
+/**
+ * gpiod_is_shared() - check if this GPIO can be shared by multiple consumers
+ * @desc: GPIO to inspect
+ *
+ * Returns:
+ * True if this GPIO can be shared by multiple consumers at once. False if it's
+ * a regular, exclusive GPIO.
+ *
+ * Note:
+ * This function returning true does not mean that this GPIO is currently being
+ * shared. It means the GPIO core has registered the fact that the firmware
+ * configuration indicates that it can be shared by multiple consumers and is
+ * in charge of arbitrating the access.
+ */
+bool gpiod_is_shared(const struct gpio_desc *desc)
+{
+	return test_bit(GPIOD_FLAG_SHARED_PROXY, &desc->flags);
+}
+EXPORT_SYMBOL_GPL(gpiod_is_shared);
+
 /**
  * gpiod_to_irq() - return the IRQ corresponding to a GPIO
  * @desc: gpio whose IRQ will be returned (already requested)
@@ -4659,11 +4688,29 @@ struct gpio_desc *gpiod_find_and_request(struct device *consumer,
 	scoped_guard(srcu, &gpio_devices_srcu) {
 		desc = gpiod_fwnode_lookup(fwnode, consumer, con_id, idx,
 					   &flags, &lookupflags);
+		if (!IS_ERR_OR_NULL(desc) &&
+		    test_bit(GPIOD_FLAG_SHARED, &desc->flags)) {
+			/*
+			 * We're dealing with a GPIO shared by multiple
+			 * consumers. This is the moment to add the machine
+			 * lookup table for the proxy device as previously
+			 * we only knew the consumer's fwnode.
+			 */
+			ret = gpio_shared_add_proxy_lookup(consumer, lookupflags);
+			if (ret)
+				return ERR_PTR(ret);
+
+			/* Trigger platform lookup for shared GPIO proxy. */
+			desc = ERR_PTR(-ENOENT);
+			/* Trigger it even for fwnode-only gpiod_get(). */
+			platform_lookup_allowed = true;
+		}
+
 		if (gpiod_not_found(desc) && platform_lookup_allowed) {
 			/*
 			 * Either we are not using DT or ACPI, or their lookup
-			 * did not return a result. In that case, use platform
+			 * did not return a result or this is a shared GPIO. In
-			 * lookup as a fallback.
+			 * that case, use platform lookup as a fallback.
 			 */
 			dev_dbg(consumer,
 				"using lookup tables for GPIO lookup\n");
@@ -4686,14 +4733,19 @@ struct gpio_desc *gpiod_find_and_request(struct device *consumer,
 			return ERR_PTR(ret);
 
 		/*
-		 * This happens when there are several consumers for
+		 * This happens when there are several consumers for the same
-		 * the same GPIO line: we just return here without
+		 * GPIO line: we just return here without further
-		 * further initialization. It is a bit of a hack.
+		 * initialization. It's a hack introduced long ago to support
-		 * This is necessary to support fixed regulators.
+		 * fixed regulators. We now have a better solution with
+		 * automated scanning where affected platforms just need to
+		 * select the provided Kconfig option.
 		 *
-		 * FIXME: Make this more sane and safe.
+		 * FIXME: Remove the GPIOD_FLAGS_BIT_NONEXCLUSIVE flag after
+		 * making sure all platforms use the new mechanism.
 		 */
-		dev_info(consumer, "nonexclusive access to GPIO for %s\n", name);
+		dev_info(consumer,
+			 "nonexclusive access to GPIO for %s, consider updating your code to using gpio-shared-proxy\n",
+			 name);
 		return desc;
 	}
 

drivers/gpio/gpiolib.h

@@ -204,6 +204,8 @@ struct gpio_desc {
 #define GPIOD_FLAG_EDGE_FALLING		17 /* GPIO CDEV detects falling edge events */
 #define GPIOD_FLAG_EVENT_CLOCK_REALTIME	18 /* GPIO CDEV reports REALTIME timestamps in events */
 #define GPIOD_FLAG_EVENT_CLOCK_HTE	19 /* GPIO CDEV reports hardware timestamps in events */
+#define GPIOD_FLAG_SHARED		20 /* GPIO is shared by multiple consumers */
+#define GPIOD_FLAG_SHARED_PROXY		21 /* GPIO is a virtual proxy to a physically shared pin. */
 
 	/* Connection label */
 	struct gpio_desc_label __rcu *label;

include/linux/gpio/consumer.h

@@ -167,6 +167,8 @@ int gpiod_cansleep(const struct gpio_desc *desc);
 int gpiod_to_irq(const struct gpio_desc *desc);
 int gpiod_set_consumer_name(struct gpio_desc *desc, const char *name);
 
+bool gpiod_is_shared(const struct gpio_desc *desc);
+
 /* Convert between the old gpio_ and new gpiod_ interfaces */
 struct gpio_desc *gpio_to_desc(unsigned gpio);
 int desc_to_gpio(const struct gpio_desc *desc);
@@ -522,6 +524,13 @@ static inline int gpiod_set_consumer_name(struct gpio_desc *desc,
 	return -EINVAL;
 }
 
+static inline bool gpiod_is_shared(const struct gpio_desc *desc)
+{
+	/* GPIO can never have been requested */
+	WARN_ON(desc);
+	return false;
+}
+
 static inline struct gpio_desc *gpio_to_desc(unsigned gpio)
 {
 	return NULL;

include/linux/string.h

@@ -562,4 +562,22 @@ static inline bool strstarts(const char *str, const char *prefix)
 	return strncmp(str, prefix, strlen(prefix)) == 0;
 }
 
+/**
+ * strends - Check if a string ends with another string.
+ * @str - NULL-terminated string to check against @suffix
+ * @suffix - NULL-terminated string defining the suffix to look for in @str
+ *
+ * Returns:
+ * True if @str ends with @suffix. False in all other cases.
+ */
+static inline bool strends(const char *str, const char *suffix)
+{
+	unsigned int str_len = strlen(str), suffix_len = strlen(suffix);
+
+	if (str_len < suffix_len)
+		return false;
+
+	return !(strcmp(str + str_len - suffix_len, suffix));
+}
+
 #endif /* _LINUX_STRING_H_ */

lib/tests/string_kunit.c

@@ -602,6 +602,18 @@ static void string_test_memtostr(struct kunit *test)
 	KUNIT_EXPECT_EQ(test, dest[7], '\0');
 }
 
+static void string_test_strends(struct kunit *test)
+{
+	KUNIT_EXPECT_TRUE(test, strends("foo-bar", "bar"));
+	KUNIT_EXPECT_TRUE(test, strends("foo-bar", "-bar"));
+	KUNIT_EXPECT_TRUE(test, strends("foobar", "foobar"));
+	KUNIT_EXPECT_TRUE(test, strends("foobar", ""));
+	KUNIT_EXPECT_FALSE(test, strends("bar", "foobar"));
+	KUNIT_EXPECT_FALSE(test, strends("", "foo"));
+	KUNIT_EXPECT_FALSE(test, strends("foobar", "ba"));
+	KUNIT_EXPECT_TRUE(test, strends("", ""));
+}
+
 static struct kunit_case string_test_cases[] = {
 	KUNIT_CASE(string_test_memset16),
 	KUNIT_CASE(string_test_memset32),
@@ -623,6 +635,7 @@ static struct kunit_case string_test_cases[] = {
 	KUNIT_CASE(string_test_strlcat),
 	KUNIT_CASE(string_test_strtomem),
 	KUNIT_CASE(string_test_memtostr),
+	KUNIT_CASE(string_test_strends),
 	{}
 };