[PATCH v3 00/10] gpio: improve support for shared GPIOs

[PATCH v3 00/10] gpio: improve support for shared GPIOs

[Bartosz Golaszewski]

Problem statement: GPIOs are implemented as a strictly exclusive
resource in the kernel but there are lots of platforms on which single
pin is shared by multiple devices which don't communicate so need some
way of properly sharing access to a GPIO. What we have now is the
GPIOD_FLAGS_BIT_NONEXCLUSIVE flag which was introduced as a hack and
doesn't do any locking or arbitration of access - it literally just hand
the same GPIO descriptor to all interested users.

The proposed solution is composed of three major parts: the high-level,
shared GPIO proxy driver that arbitrates access to the shared pin and
exposes a regular GPIO chip interface to consumers, a low-level shared
GPIOLIB module that scans firmware nodes and creates auxiliary devices
that attach to the proxy driver and finally a set of core GPIOLIB
changes that plug the former into the GPIO lookup path.

The changes are implemented in a way that allows to seamlessly compile
out any code related to sharing GPIOs for systems that don't need it.

The practical use-case for this are the powerdown GPIOs shared by
speakers on Qualcomm db845c platform, however I have also extensively
tested it using gpio-virtuser on arm64 qemu with various DT
configurations.

I'm Cc'ing some people that may help with reviewing/be interested in
this: OF maintainers (because the main target are OF systems initially),
Mark Brown because most users of GPIOD_FLAGS_BIT_NONEXCLUSIVE live
in audio or regulator drivers and one of the goals of this series is
dropping the hand-crafted GPIO enable counting via struct
regulator_enable_gpio in regulator core), Andy and Mika because I'd like
to also cover ACPI (even though I don't know about any ACPI platform that
would need this at the moment, I think it makes sense to make the
solution complete), Dmitry (same thing but for software nodes), Mani
(because you have a somewhat related use-case for the PERST# signal and
I'd like to hear your input on whether this is something you can use or
maybe it needs a separate, implicit gpio-perst driver similar to what
Krzysztof did for reset-gpios) and Greg (because I mentioned this to you
last week in person and I also use the auxiliary bus for the proxy
devices).

Merging strategy: patches 1-6 should go through the GPIO tree and then
ARM-SoC, ASoC and regulator trees can pull these changes from an
immutable branch and apply the remaining patches.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
Changes in v3:
- Make strends() a static inline function
- Use an empty release() callback for auxiliary devices
- Refactor the code for finding the shared descriptors in the GPIOLIB
  shared module, split it into several smaller functions
- Use str_high_low() where applicable
- Use non-atomic bit ops where atomicity is not required
- Link to v2: https://lore.kernel.org/r/20251022-gpio-shared-v2-0-d34aa1fbdf06@linaro.org

Changes in v2:
- Fix a memory leak in error path in gpiolib-shared
- Drop the gpio-wcd934x fix that already went upstream
- Free resources used during scanning by GPIOs that turned out to be
  unique
- Rework the OF property scanning
- Add patches making the regulator subsystem aware of shared GPIOs
  managed by GPIOLIB
- Link to v1: https://lore.kernel.org/r/20250924-gpio-shared-v1-0-775e7efeb1a3@linaro.org

---
Bartosz Golaszewski (10):
      string: provide strends()
      gpiolib: define GPIOD_FLAG_SHARED
      gpiolib: implement low-level, shared GPIO support
      gpio: shared-proxy: implement the shared GPIO proxy driver
      gpiolib: support shared GPIOs in core subsystem code
      gpio: provide gpiod_is_shared()
      arm64: select HAVE_SHARED_GPIOS for ARCH_QCOM
      ASoC: wsa881x: drop GPIOD_FLAGS_BIT_NONEXCLUSIVE flag from GPIO lookup
      ASoC: wsa883x: drop GPIOD_FLAGS_BIT_NONEXCLUSIVE flag from GPIO lookup
      regulator: make the subsystem aware of shared GPIOs

 arch/arm64/Kconfig.platforms     |   1 +
 drivers/gpio/Kconfig             |  17 ++
 drivers/gpio/Makefile            |   2 +
 drivers/gpio/gpio-shared-proxy.c | 333 +++++++++++++++++++++++
 drivers/gpio/gpiolib-shared.c    | 558 +++++++++++++++++++++++++++++++++++++++
 drivers/gpio/gpiolib-shared.h    |  71 +++++
 drivers/gpio/gpiolib.c           |  70 ++++-
 drivers/gpio/gpiolib.h           |   2 +
 drivers/regulator/core.c         |   8 +
 include/linux/gpio/consumer.h    |   9 +
 include/linux/string.h           |  18 ++
 lib/tests/string_kunit.c         |  13 +
 sound/soc/codecs/wsa881x.c       |   3 +-
 sound/soc/codecs/wsa883x.c       |   7 +-
 14 files changed, 1096 insertions(+), 16 deletions(-)
---
base-commit: 2a3cf7aa49244fafeedf9f334d3e88fe8ee05b50
change-id: 20250908-gpio-shared-67ec352884b6

Best regards,
-- 
Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

[PATCH v3 01/10] string: provide strends()

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Implement a function for checking if a string ends with a different
string and add its kunit test cases.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 include/linux/string.h   | 18 ++++++++++++++++++
 lib/tests/string_kunit.c | 13 +++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/include/linux/string.h b/include/linux/string.h
index fdd3442c6bcbd786e177b6e87358e1065a0ffafc..929d05d1247c76eb9011fe34250b487834b2d3c9 100644
--- a/include/linux/string.h
+++ b/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_ */
diff --git a/lib/tests/string_kunit.c b/lib/tests/string_kunit.c
index 0ed7448a26d3aa0fe9e2a6a894d4c49c2c0b86e0..f9a8e557ba7734c9848d58ff986407d8000f52ee 100644
--- a/lib/tests/string_kunit.c
+++ b/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),
 	{}
 };
 

-- 
2.48.1

Re: [PATCH v3 01/10] string: provide strends()

[Andy Shevchenko]

On Wed, Oct 29, 2025 at 12:20:37PM +0100, Bartosz Golaszewski wrote:
> 
> Implement a function for checking if a string ends with a different
> string and add its kunit test cases.

...

> +/**
> + * 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));
> +}

Can you rather re-use strcmp_suffix() from drivers/of/property.c?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v3 01/10] string: provide strends()

[Bartosz Golaszewski]

On Wed, Oct 29, 2025 at 12:42 PM Andy Shevchenko
<andriy.shevchenko@intel.com> wrote:
>
> On Wed, Oct 29, 2025 at 12:20:37PM +0100, Bartosz Golaszewski wrote:
> >
> > Implement a function for checking if a string ends with a different
> > string and add its kunit test cases.
>
> ...
>
> > +/**
> > + * 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));
> > +}
>
> Can you rather re-use strcmp_suffix() from drivers/of/property.c?
>

I think that strends() and its boolean return value are a bit more
intuitive to use than strcmp_suffix() and its integer return value,
the meaning of which you typically have to look-up to figure out. If
there are no objections, I'd like to keep it and - when it's upstream
- convert property.c to using it instead. Also: the name
strcmp_suffix() could use some improvement, seeing how I wasn't able
to find it, even though I looked hard across the kernel source, while
I easily stumbled upon a similar implementation of strends() already
existing in dtc sources.

Bart

Re: [PATCH v3 01/10] string: provide strends()

[Andy Shevchenko]

On Wed, Oct 29, 2025 at 01:36:55PM +0100, Bartosz Golaszewski wrote:
> On Wed, Oct 29, 2025 at 12:42 PM Andy Shevchenko
> <andriy.shevchenko@intel.com> wrote:
> > On Wed, Oct 29, 2025 at 12:20:37PM +0100, Bartosz Golaszewski wrote:

...

> > Can you rather re-use strcmp_suffix() from drivers/of/property.c?
> 
> I think that strends() and its boolean return value are a bit more
> intuitive to use than strcmp_suffix() and its integer return value,
> the meaning of which you typically have to look-up to figure out. If
> there are no objections, I'd like to keep it and - when it's upstream
> - convert property.c to using it instead. Also: the name
> strcmp_suffix() could use some improvement, seeing how I wasn't able
> to find it, even though I looked hard across the kernel source, while
> I easily stumbled upon a similar implementation of strends() already
> existing in dtc sources.

I fine as long as the replacement (deduplication) change is provided.

-- 
With Best Regards,
Andy Shevchenko

[PATCH v3 02/10] gpiolib: define GPIOD_FLAG_SHARED

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Define a new GPIO descriptor flag for marking pins that are shared by
multiple consumer. This flag will be used in several places so we need
to do it in advance and separately from other changes.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 drivers/gpio/gpiolib.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index 14e6a9807a89da6d7c6594a0a2de5f5032c49e0d..c9de4bb10584206f4888c0f28468762a3680aae6 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -204,6 +204,7 @@ 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 */
 
 	/* Connection label */
 	struct gpio_desc_label __rcu *label;

-- 
2.48.1

Re: [PATCH v3 02/10] gpiolib: define GPIOD_FLAG_SHARED

[Linus Walleij]

On Wed, Oct 29, 2025 at 12:21 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:

> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> Define a new GPIO descriptor flag for marking pins that are shared by
> multiple consumer. This flag will be used in several places so we need
> to do it in advance and separately from other changes.
>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij

[PATCH v3 03/10] gpiolib: implement low-level, shared GPIO support

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

This module scans the device tree (for now only OF nodes are supported
but care is taken to make other fwnode implementations easy to
integrate) and determines which GPIO lines are shared by multiple users.
It stores that information in memory. When the GPIO chip exposing shared
lines is registered, the shared GPIO descriptors it exposes are marked
as shared and virtual "proxy" devices that mediate access to the shared
lines are created. When a consumer of a shared GPIO looks it up, its
fwnode lookup is redirected to a just-in-time machine lookup that points
to this proxy device.

This code can be compiled out on platforms which don't use shared GPIOs.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 drivers/gpio/Kconfig          |   8 +
 drivers/gpio/Makefile         |   1 +
 drivers/gpio/gpiolib-shared.c | 540 ++++++++++++++++++++++++++++++++++++++++++
 drivers/gpio/gpiolib-shared.h |  71 ++++++
 4 files changed, 620 insertions(+)

diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index ce237398fa00eddad49afe995accae3abbb4b2cb..f90b4d3e77f7cab46525b7adfcf114a21d276678 100644
--- a/drivers/gpio/Kconfig
+++ b/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
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index ee260a0809d36cd07987f04e0ef17b05af764214..48f309c764e3286c23dbe604be933f7180f0b89a 100644
--- a/drivers/gpio/Makefile
+++ b/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
diff --git a/drivers/gpio/gpiolib-shared.c b/drivers/gpio/gpiolib-shared.c
new file mode 100644
index 0000000000000000000000000000000000000000..56b9b03cbb6dbcdf095a656fc36ff321770035da
--- /dev/null
+++ b/drivers/gpio/gpiolib-shared.c
@@ -0,0 +1,540 @@
+// 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) {
+		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);
diff --git a/drivers/gpio/gpiolib-shared.h b/drivers/gpio/gpiolib-shared.h
new file mode 100644
index 0000000000000000000000000000000000000000..667dbdff3585066b7cbe2ebe476725fe7d683d84
--- /dev/null
+++ b/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 */

-- 
2.48.1

Re: [PATCH v3 03/10] gpiolib: implement low-level, shared GPIO support

[Andy Shevchenko]

On Wed, Oct 29, 2025 at 12:20:39PM +0100, Bartosz Golaszewski wrote:
> 
> This module scans the device tree (for now only OF nodes are supported
> but care is taken to make other fwnode implementations easy to
> integrate) and determines which GPIO lines are shared by multiple users.
> It stores that information in memory. When the GPIO chip exposing shared
> lines is registered, the shared GPIO descriptors it exposes are marked
> as shared and virtual "proxy" devices that mediate access to the shared
> lines are created. When a consumer of a shared GPIO looks it up, its
> fwnode lookup is redirected to a just-in-time machine lookup that points
> to this proxy device.
> 
> This code can be compiled out on platforms which don't use shared GPIOs.

Besides strcmp_suffix() that already exists in OF core, there are also some
existing pieces that seems being repeated here (again). Can we reduce amount
of duplication?

...

> +#if IS_ENABLED(CONFIG_OF)
> +static int gpio_shared_of_traverse(struct device_node *curr)
> +{

I believe parts of this code may be resided somewhere in drivers/of/property.c
or nearby as it has the similar parsing routines.

> +	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;
> +}

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v3 03/10] gpiolib: implement low-level, shared GPIO support

[Bartosz Golaszewski]

On Wed, Oct 29, 2025 at 12:45 PM Andy Shevchenko
<andriy.shevchenko@intel.com> wrote:
>
> On Wed, Oct 29, 2025 at 12:20:39PM +0100, Bartosz Golaszewski wrote:
> >
> > This module scans the device tree (for now only OF nodes are supported
> > but care is taken to make other fwnode implementations easy to
> > integrate) and determines which GPIO lines are shared by multiple users.
> > It stores that information in memory. When the GPIO chip exposing shared
> > lines is registered, the shared GPIO descriptors it exposes are marked
> > as shared and virtual "proxy" devices that mediate access to the shared
> > lines are created. When a consumer of a shared GPIO looks it up, its
> > fwnode lookup is redirected to a just-in-time machine lookup that points
> > to this proxy device.
> >
> > This code can be compiled out on platforms which don't use shared GPIOs.
>
> Besides strcmp_suffix() that already exists in OF core, there are also some
> existing pieces that seems being repeated here (again). Can we reduce amount
> of duplication?
>

I'm afraid you need to be more specific here.

> ...
>
> > +#if IS_ENABLED(CONFIG_OF)
> > +static int gpio_shared_of_traverse(struct device_node *curr)
> > +{
>
> I believe parts of this code may be resided somewhere in drivers/of/property.c
> or nearby as it has the similar parsing routines.
>

I don't think this is a good idea, I want to keep it within the
confines of drivers/gpio/ and the use-case is so specific, there's
really no point in putting parts of it under drivers/of/.

If I could only iterate over all properties of an fwnode, I'd have
skipped using OF-specific routines altogether.

Bart

Re: [PATCH v3 03/10] gpiolib: implement low-level, shared GPIO support

[Andy Shevchenko]

On Wed, Oct 29, 2025 at 01:39:34PM +0100, Bartosz Golaszewski wrote:
> On Wed, Oct 29, 2025 at 12:45 PM Andy Shevchenko
> <andriy.shevchenko@intel.com> wrote:
> > On Wed, Oct 29, 2025 at 12:20:39PM +0100, Bartosz Golaszewski wrote:
> > >
> > > This module scans the device tree (for now only OF nodes are supported
> > > but care is taken to make other fwnode implementations easy to
> > > integrate) and determines which GPIO lines are shared by multiple users.
> > > It stores that information in memory. When the GPIO chip exposing shared
> > > lines is registered, the shared GPIO descriptors it exposes are marked
> > > as shared and virtual "proxy" devices that mediate access to the shared
> > > lines are created. When a consumer of a shared GPIO looks it up, its
> > > fwnode lookup is redirected to a just-in-time machine lookup that points
> > > to this proxy device.
> > >
> > > This code can be compiled out on platforms which don't use shared GPIOs.
> >
> > Besides strcmp_suffix() that already exists in OF core, there are also some
> > existing pieces that seems being repeated here (again). Can we reduce amount
> > of duplication?
> 
> I'm afraid you need to be more specific here.

You can simply browse the file, it's not long to find and think about it.
I'm _thinking_ that it's possible to improve the situation overall by
try our best of deduplicating (or rather not duplicating) things.

...

> > > +#if IS_ENABLED(CONFIG_OF)
> > > +static int gpio_shared_of_traverse(struct device_node *curr)
> > > +{
> >
> > I believe parts of this code may be resided somewhere in drivers/of/property.c
> > or nearby as it has the similar parsing routines.
> 
> I don't think this is a good idea, I want to keep it within the
> confines of drivers/gpio/ and the use-case is so specific, there's
> really no point in putting parts of it under drivers/of/.
> 
> If I could only iterate over all properties of an fwnode, I'd have
> skipped using OF-specific routines altogether.

The problem is that every subsystem considers "it's not a good idea" or
"historical reasons" or other excuses. Since you are adding OF-specific
stuff that has something already done inside OF specific code, why to
spread it over the kernel by duplicating in another place(s)?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v3 03/10] gpiolib: implement low-level, shared GPIO support

[Bartosz Golaszewski]

On Wed, Oct 29, 2025 at 4:19 PM Andy Shevchenko
<andriy.shevchenko@intel.com> wrote:
>
> On Wed, Oct 29, 2025 at 01:39:34PM +0100, Bartosz Golaszewski wrote:
> > On Wed, Oct 29, 2025 at 12:45 PM Andy Shevchenko
> > <andriy.shevchenko@intel.com> wrote:
> > > On Wed, Oct 29, 2025 at 12:20:39PM +0100, Bartosz Golaszewski wrote:
> > > >
> > > > This module scans the device tree (for now only OF nodes are supported
> > > > but care is taken to make other fwnode implementations easy to
> > > > integrate) and determines which GPIO lines are shared by multiple users.
> > > > It stores that information in memory. When the GPIO chip exposing shared
> > > > lines is registered, the shared GPIO descriptors it exposes are marked
> > > > as shared and virtual "proxy" devices that mediate access to the shared
> > > > lines are created. When a consumer of a shared GPIO looks it up, its
> > > > fwnode lookup is redirected to a just-in-time machine lookup that points
> > > > to this proxy device.
> > > >
> > > > This code can be compiled out on platforms which don't use shared GPIOs.
> > >
> > > Besides strcmp_suffix() that already exists in OF core, there are also some
> > > existing pieces that seems being repeated here (again). Can we reduce amount
> > > of duplication?
> >
> > I'm afraid you need to be more specific here.
>
> You can simply browse the file, it's not long to find and think about it.
> I'm _thinking_ that it's possible to improve the situation overall by
> try our best of deduplicating (or rather not duplicating) things.
>

Sorry, but this is not how reviewing works. You can't just say: "I
think this can be improved, go figure out what can and fix it, you can
browse this file for reference". You need to specifically point out
issues in code and propose alternatives.

> ...
>
> > > > +#if IS_ENABLED(CONFIG_OF)
> > > > +static int gpio_shared_of_traverse(struct device_node *curr)
> > > > +{
> > >
> > > I believe parts of this code may be resided somewhere in drivers/of/property.c
> > > or nearby as it has the similar parsing routines.
> >
> > I don't think this is a good idea, I want to keep it within the
> > confines of drivers/gpio/ and the use-case is so specific, there's
> > really no point in putting parts of it under drivers/of/.
> >
> > If I could only iterate over all properties of an fwnode, I'd have
> > skipped using OF-specific routines altogether.
>
> The problem is that every subsystem considers "it's not a good idea" or
> "historical reasons" or other excuses. Since you are adding OF-specific
> stuff that has something already done inside OF specific code, why to
> spread it over the kernel by duplicating in another place(s)?
>

Well, point me to the things that have been done already and I'll see
about reusing them.

Bartosz

Re: [PATCH v3 03/10] gpiolib: implement low-level, shared GPIO support

[Andy Shevchenko]

On Wed, Oct 29, 2025 at 04:57:02PM +0100, Bartosz Golaszewski wrote:
> On Wed, Oct 29, 2025 at 4:19 PM Andy Shevchenko
> <andriy.shevchenko@intel.com> wrote:
> > On Wed, Oct 29, 2025 at 01:39:34PM +0100, Bartosz Golaszewski wrote:
> > > On Wed, Oct 29, 2025 at 12:45 PM Andy Shevchenko
> > > <andriy.shevchenko@intel.com> wrote:
> > > > On Wed, Oct 29, 2025 at 12:20:39PM +0100, Bartosz Golaszewski wrote:

...

> > > > Besides strcmp_suffix() that already exists in OF core, there are also some
> > > > existing pieces that seems being repeated here (again). Can we reduce amount
> > > > of duplication?
> > >
> > > I'm afraid you need to be more specific here.
> >
> > You can simply browse the file, it's not long to find and think about it.
> > I'm _thinking_ that it's possible to improve the situation overall by
> > try our best of deduplicating (or rather not duplicating) things.
> 
> Sorry, but this is not how reviewing works. You can't just say: "I
> think this can be improved, go figure out what can and fix it, you can
> browse this file for reference". You need to specifically point out
> issues in code and propose alternatives.

Then consider this as a hint and not a review.

...

> > > > > +#if IS_ENABLED(CONFIG_OF)
> > > > > +static int gpio_shared_of_traverse(struct device_node *curr)
> > > > > +{
> > > >
> > > > I believe parts of this code may be resided somewhere in drivers/of/property.c
> > > > or nearby as it has the similar parsing routines.
> > >
> > > I don't think this is a good idea, I want to keep it within the
> > > confines of drivers/gpio/ and the use-case is so specific, there's
> > > really no point in putting parts of it under drivers/of/.
> > >
> > > If I could only iterate over all properties of an fwnode, I'd have
> > > skipped using OF-specific routines altogether.
> >
> > The problem is that every subsystem considers "it's not a good idea" or
> > "historical reasons" or other excuses. Since you are adding OF-specific
> > stuff that has something already done inside OF specific code, why to
> > spread it over the kernel by duplicating in another place(s)?
> 
> Well, point me to the things that have been done already and I'll see
> about reusing them.

I already gave a direction, but if you think the duplication is okay, up to
you. It can be addressed later, just a bit more of technical debt.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v3 03/10] gpiolib: implement low-level, shared GPIO support

[Linus Walleij]

On Wed, Oct 29, 2025 at 12:21 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:

> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> This module scans the device tree (for now only OF nodes are supported
> but care is taken to make other fwnode implementations easy to
> integrate) and determines which GPIO lines are shared by multiple users.
> It stores that information in memory. When the GPIO chip exposing shared
> lines is registered, the shared GPIO descriptors it exposes are marked
> as shared and virtual "proxy" devices that mediate access to the shared
> lines are created. When a consumer of a shared GPIO looks it up, its
> fwnode lookup is redirected to a just-in-time machine lookup that points
> to this proxy device.
>
> This code can be compiled out on platforms which don't use shared GPIOs.
>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

The concept is sound and we have to begin somewhere, optimizations
for code reuse and cleanups can be done in-tree.

So:

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij

[PATCH v3 04/10] gpio: shared-proxy: implement the shared GPIO proxy driver

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Add a virtual GPIO proxy driver which arbitrates access to a single
shared GPIO by multiple users. It works together with the core shared
GPIO support from GPIOLIB and functions by acquiring a reference to a
shared GPIO descriptor exposed by gpiolib-shared and making sure that
the state of the GPIO stays consistent.

In general: if there's only one user at the moment: allow it to do
anything as if this was a normal GPIO (in essence: just propagate calls
to the underlying real hardware driver). If there are more users: don't
allow to change the direction set by the initial user, allow to change
configuration options but warn about possible conflicts and finally:
treat the output-high value as a reference counted, logical "GPIO
enabled" setting, meaning: the GPIO value is set to high when the first
user requests it to be high and back to low once the last user stops
"voting" for high.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 drivers/gpio/Kconfig             |   9 ++
 drivers/gpio/Makefile            |   1 +
 drivers/gpio/gpio-shared-proxy.c | 333 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 343 insertions(+)

diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index f90b4d3e77f7cab46525b7adfcf114a21d276678..f910c20f0d5d7771f7f8f3d52ced7bce413d24f1 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -2025,6 +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"
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index 48f309c764e3286c23dbe604be933f7180f0b89a..2421a8fd3733e0b06c2581262aaa9cd629f66c7d 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -161,6 +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
diff --git a/drivers/gpio/gpio-shared-proxy.c b/drivers/gpio/gpio-shared-proxy.c
new file mode 100644
index 0000000000000000000000000000000000000000..3ef2c40ed15229074052eda93b6ee56f0a2bfb72
--- /dev/null
+++ b/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");

-- 
2.48.1

Re: [PATCH v3 04/10] gpio: shared-proxy: implement the shared GPIO proxy driver

[Linus Walleij]

On Wed, Oct 29, 2025 at 12:21 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:

> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> Add a virtual GPIO proxy driver which arbitrates access to a single
> shared GPIO by multiple users. It works together with the core shared
> GPIO support from GPIOLIB and functions by acquiring a reference to a
> shared GPIO descriptor exposed by gpiolib-shared and making sure that
> the state of the GPIO stays consistent.
>
> In general: if there's only one user at the moment: allow it to do
> anything as if this was a normal GPIO (in essence: just propagate calls
> to the underlying real hardware driver). If there are more users: don't
> allow to change the direction set by the initial user, allow to change
> configuration options but warn about possible conflicts and finally:
> treat the output-high value as a reference counted, logical "GPIO
> enabled" setting, meaning: the GPIO value is set to high when the first
> user requests it to be high and back to low once the last user stops
> "voting" for high.
>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

With same reasoning as for 3/10:
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij

[PATCH v3 05/10] gpiolib: support shared GPIOs in core subsystem code

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

As the final step in adding official support for shared GPIOs, enable
the previously added elements in core GPIO subsystem code. Set-up shared
GPIOs when adding a GPIO chip, tear it down on removal and check if a
GPIO descriptor looked up during the firmware-node stage is shared and
fall-back to machine lookup in this case.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 drivers/gpio/gpiolib.c | 50 +++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 41 insertions(+), 9 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index a81981336b36db49d899634feafcd9bc25edf96f..c0c0e9370f150c340a7c79dc03c5afec64a440f4 100644
--- a/drivers/gpio/gpiolib.c
+++ b/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);
@@ -4659,11 +4668,29 @@ 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
-			 * lookup as a fallback.
+			 * did not return a result or this is a shared GPIO. In
+			 * that case, use platform lookup as a fallback.
 			 */
 			dev_dbg(consumer,
 				"using lookup tables for GPIO lookup\n");
@@ -4686,14 +4713,19 @@ struct gpio_desc *gpiod_find_and_request(struct device *consumer,
 			return ERR_PTR(ret);
 
 		/*
-		 * This happens when there are several consumers for
-		 * the same GPIO line: we just return here without
-		 * further initialization. It is a bit of a hack.
-		 * This is necessary to support fixed regulators.
+		 * This happens when there are several consumers for the same
+		 * GPIO line: we just return here without further
+		 * initialization. It's a hack introduced long ago to support
+		 * 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;
 	}
 

-- 
2.48.1

Re: [PATCH v3 05/10] gpiolib: support shared GPIOs in core subsystem code

[Linus Walleij]

On Wed, Oct 29, 2025 at 12:21 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:

> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> As the final step in adding official support for shared GPIOs, enable
> the previously added elements in core GPIO subsystem code. Set-up shared
> GPIOs when adding a GPIO chip, tear it down on removal and check if a
> GPIO descriptor looked up during the firmware-node stage is shared and
> fall-back to machine lookup in this case.
>
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij

[PATCH v3 06/10] gpio: provide gpiod_is_shared()

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Provide an interface allowing consumers to check if a GPIO descriptor
represents a GPIO that can potentially be shared by multiple consumers
at the same time. This is exposed to allow subsystems that already
work around the limitations of the current non-exclusive GPIO handling
in some ways, to gradually convert to relying on the new shared GPIO
feature of GPIOLIB.

Extend the gpiolib-shared module to mark the GPIO shared proxy
descriptors with a flag checked by the new interface.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 drivers/gpio/gpiolib-shared.c | 18 ++++++++++++++++++
 drivers/gpio/gpiolib.c        | 20 ++++++++++++++++++++
 drivers/gpio/gpiolib.h        |  1 +
 include/linux/gpio/consumer.h |  9 +++++++++
 4 files changed, 48 insertions(+)

diff --git a/drivers/gpio/gpiolib-shared.c b/drivers/gpio/gpiolib-shared.c
index 56b9b03cbb6dbcdf095a656fc36ff321770035da..c22eaf05eef23a7f5f111708c3db9412c4c30231 100644
--- a/drivers/gpio/gpiolib-shared.c
+++ b/drivers/gpio/gpiolib-shared.c
@@ -314,6 +314,24 @@ int gpio_device_setup_shared(struct gpio_device *gdev)
 
 	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;
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index c0c0e9370f150c340a7c79dc03c5afec64a440f4..fb4311d41161051dfd3c996b6e8e9e8556b97cbc 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -3997,6 +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)
diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
index c9de4bb10584206f4888c0f28468762a3680aae6..77f6f2936dc263a67b31a38799a841128a57603a 100644
--- a/drivers/gpio/gpiolib.h
+++ b/drivers/gpio/gpiolib.h
@@ -205,6 +205,7 @@ struct gpio_desc {
 #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;
diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
index 994d46874d560416175c9099e18180237839bd4c..cafeb7a40ad1c25aeb7deaf598410d5f2f004a82 100644
--- a/include/linux/gpio/consumer.h
+++ b/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;

-- 
2.48.1

[PATCH v3 07/10] arm64: select HAVE_SHARED_GPIOS for ARCH_QCOM

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Some qualcomm platforms use shared GPIOs. Enable support for them by
selecting the Kconfig switch provided by GPIOLIB.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 arch/arm64/Kconfig.platforms | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/Kconfig.platforms b/arch/arm64/Kconfig.platforms
index 13173795c43d4f28e2d47acc700f80a165d44671..3dbff0261f0add0516d8cb3fd0f29e277af94f20 100644
--- a/arch/arm64/Kconfig.platforms
+++ b/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.
 

-- 
2.48.1

[PATCH v3 08/10] ASoC: wsa881x: drop GPIOD_FLAGS_BIT_NONEXCLUSIVE flag from GPIO lookup

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

This driver is only used on Qualcomm platforms which now select
HAVE_SHARED_GPIOS so this flag can be dropped.

Reviewed-and-tested-by: Alexey Klimov <alexey.klimov@linaro.org> # RB3
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 sound/soc/codecs/wsa881x.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/sound/soc/codecs/wsa881x.c b/sound/soc/codecs/wsa881x.c
index e249de7f91d91f8c7f1e7020086cc65c71e64c5e..d7aca6567c2de1ec36e9f36aa82463bdbf3be27e 100644
--- a/sound/soc/codecs/wsa881x.c
+++ b/sound/soc/codecs/wsa881x.c
@@ -1112,8 +1112,7 @@ static int wsa881x_probe(struct sdw_slave *pdev,
 	if (!wsa881x)
 		return -ENOMEM;
 
-	wsa881x->sd_n = devm_gpiod_get_optional(dev, "powerdown",
-						GPIOD_FLAGS_BIT_NONEXCLUSIVE);
+	wsa881x->sd_n = devm_gpiod_get_optional(dev, "powerdown", 0);
 	if (IS_ERR(wsa881x->sd_n))
 		return dev_err_probe(dev, PTR_ERR(wsa881x->sd_n),
 				     "Shutdown Control GPIO not found\n");

-- 
2.48.1

[PATCH v3 09/10] ASoC: wsa883x: drop GPIOD_FLAGS_BIT_NONEXCLUSIVE flag from GPIO lookup

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

This driver is only used on Qualcomm platforms which now select
HAVE_SHARED_GPIOS so this flag can be dropped.

Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 sound/soc/codecs/wsa883x.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/sound/soc/codecs/wsa883x.c b/sound/soc/codecs/wsa883x.c
index 96dd66c4b88dea34f1f24bed4d5ab66d3e2249ae..c3046e260cb958296a41b78b545f1ac7f377a968 100644
--- a/sound/soc/codecs/wsa883x.c
+++ b/sound/soc/codecs/wsa883x.c
@@ -1572,13 +1572,10 @@ static int wsa883x_get_reset(struct device *dev, struct wsa883x_priv *wsa883x)
 	if (IS_ERR(wsa883x->sd_reset))
 		return dev_err_probe(dev, PTR_ERR(wsa883x->sd_reset),
 				     "Failed to get reset\n");
-	/*
-	 * if sd_reset: NULL, so use the backwards compatible way for powerdown-gpios,
-	 * which does not handle sharing GPIO properly.
-	 */
+
+	 /* if sd_reset: NULL, so use the backwards compatible way for powerdown-gpios */
 	if (!wsa883x->sd_reset) {
 		wsa883x->sd_n = devm_gpiod_get_optional(dev, "powerdown",
-							GPIOD_FLAGS_BIT_NONEXCLUSIVE |
 							GPIOD_OUT_HIGH);
 		if (IS_ERR(wsa883x->sd_n))
 			return dev_err_probe(dev, PTR_ERR(wsa883x->sd_n),

-- 
2.48.1

[PATCH v3 10/10] regulator: make the subsystem aware of shared GPIOs

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

GPIOLIB is now aware of shared GPIOs and - for platforms where access to
such pins is managed internally - we don't need to keep track of the
enable count.

Once all users in the kernel switch to using the new mechanism, we'll be
able to drop the internal counting of users from the regulator code.

Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 drivers/regulator/core.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 84bc38911dba308539a25dd3af30a5c24802b890..e13cf5e120466cebc4d3f8400b89be07d3303338 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -2737,6 +2737,13 @@ static int regulator_ena_gpio_request(struct regulator_dev *rdev,
 
 	mutex_lock(&regulator_list_mutex);
 
+	if (gpiod_is_shared(gpiod))
+		/*
+		 * The sharing of this GPIO pin is managed internally by
+		 * GPIOLIB. We don't need to keep track of its enable count.
+		 */
+		goto skip_compare;
+
 	list_for_each_entry(pin, &regulator_ena_gpio_list, list) {
 		if (gpiod_is_equal(pin->gpiod, gpiod)) {
 			rdev_dbg(rdev, "GPIO is already used\n");
@@ -2749,6 +2756,7 @@ static int regulator_ena_gpio_request(struct regulator_dev *rdev,
 		return -ENOMEM;
 	}
 
+skip_compare:
 	pin = new_pin;
 	new_pin = NULL;
 

-- 
2.48.1

Re: [PATCH v3 10/10] regulator: make the subsystem aware of shared GPIOs

[Andy Shevchenko]

On Wed, Oct 29, 2025 at 12:20:46PM +0100, Bartosz Golaszewski wrote:
> 
> GPIOLIB is now aware of shared GPIOs and - for platforms where access to
> such pins is managed internally - we don't need to keep track of the
> enable count.
> 
> Once all users in the kernel switch to using the new mechanism, we'll be
> able to drop the internal counting of users from the regulator code.

I am wondering if you took into account the layering violation (or others
put it as "transferring of ownership") in the regulator core for the platform
based GPIO regulators? This popped up during the discussion of
https://lore.kernel.org/platform-driver-x86/20251024050537.92440-1-qiuwenbo@gnome.org/

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v3 10/10] regulator: make the subsystem aware of shared GPIOs

[Bartosz Golaszewski]

On Wed, Oct 29, 2025 at 12:54 PM Andy Shevchenko
<andriy.shevchenko@intel.com> wrote:
>
> On Wed, Oct 29, 2025 at 12:20:46PM +0100, Bartosz Golaszewski wrote:
> >
> > GPIOLIB is now aware of shared GPIOs and - for platforms where access to
> > such pins is managed internally - we don't need to keep track of the
> > enable count.
> >
> > Once all users in the kernel switch to using the new mechanism, we'll be
> > able to drop the internal counting of users from the regulator code.
>
> I am wondering if you took into account the layering violation (or others
> put it as "transferring of ownership") in the regulator core for the platform
> based GPIO regulators? This popped up during the discussion of
> https://lore.kernel.org/platform-driver-x86/20251024050537.92440-1-qiuwenbo@gnome.org/
>

I am aware of this weird ownership transfer in regulator but these
changes don't affect it. The layering is still being violated though.

This should be fixed and I've looked into it but it's not trivial so
it's another big rework for the future.

Bart

Re: [PATCH v3 10/10] regulator: make the subsystem aware of shared GPIOs

[Andy Shevchenko]

On Wed, Oct 29, 2025 at 01:41:10PM +0100, Bartosz Golaszewski wrote:
> On Wed, Oct 29, 2025 at 12:54 PM Andy Shevchenko
> <andriy.shevchenko@intel.com> wrote:
> > On Wed, Oct 29, 2025 at 12:20:46PM +0100, Bartosz Golaszewski wrote:
> > >
> > > GPIOLIB is now aware of shared GPIOs and - for platforms where access to
> > > such pins is managed internally - we don't need to keep track of the
> > > enable count.
> > >
> > > Once all users in the kernel switch to using the new mechanism, we'll be
> > > able to drop the internal counting of users from the regulator code.
> >
> > I am wondering if you took into account the layering violation (or others
> > put it as "transferring of ownership") in the regulator core for the platform
> > based GPIO regulators? This popped up during the discussion of
> > https://lore.kernel.org/platform-driver-x86/20251024050537.92440-1-qiuwenbo@gnome.org/
> 
> I am aware of this weird ownership transfer in regulator but these
> changes don't affect it. The layering is still being violated though.
> 
> This should be fixed and I've looked into it but it's not trivial so
> it's another big rework for the future.

OK, thanks for clarifications!

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v3 00/10] gpio: improve support for shared GPIOs

[Bartosz Golaszewski]

On Wed, Oct 29, 2025 at 12:20 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
>
> Problem statement: GPIOs are implemented as a strictly exclusive
> resource in the kernel but there are lots of platforms on which single
> pin is shared by multiple devices which don't communicate so need some
> way of properly sharing access to a GPIO. What we have now is the
> GPIOD_FLAGS_BIT_NONEXCLUSIVE flag which was introduced as a hack and
> doesn't do any locking or arbitration of access - it literally just hand
> the same GPIO descriptor to all interested users.
>
> The proposed solution is composed of three major parts: the high-level,
> shared GPIO proxy driver that arbitrates access to the shared pin and
> exposes a regular GPIO chip interface to consumers, a low-level shared
> GPIOLIB module that scans firmware nodes and creates auxiliary devices
> that attach to the proxy driver and finally a set of core GPIOLIB
> changes that plug the former into the GPIO lookup path.
>
> The changes are implemented in a way that allows to seamlessly compile
> out any code related to sharing GPIOs for systems that don't need it.
>
> The practical use-case for this are the powerdown GPIOs shared by
> speakers on Qualcomm db845c platform, however I have also extensively
> tested it using gpio-virtuser on arm64 qemu with various DT
> configurations.
>
> I'm Cc'ing some people that may help with reviewing/be interested in
> this: OF maintainers (because the main target are OF systems initially),
> Mark Brown because most users of GPIOD_FLAGS_BIT_NONEXCLUSIVE live
> in audio or regulator drivers and one of the goals of this series is
> dropping the hand-crafted GPIO enable counting via struct
> regulator_enable_gpio in regulator core), Andy and Mika because I'd like
> to also cover ACPI (even though I don't know about any ACPI platform that
> would need this at the moment, I think it makes sense to make the
> solution complete), Dmitry (same thing but for software nodes), Mani
> (because you have a somewhat related use-case for the PERST# signal and
> I'd like to hear your input on whether this is something you can use or
> maybe it needs a separate, implicit gpio-perst driver similar to what
> Krzysztof did for reset-gpios) and Greg (because I mentioned this to you
> last week in person and I also use the auxiliary bus for the proxy
> devices).
>
> Merging strategy: patches 1-6 should go through the GPIO tree and then
> ARM-SoC, ASoC and regulator trees can pull these changes from an
> immutable branch and apply the remaining patches.
>

Can I get some Reviewed-bys under the GPIO patches if there are no
other open issues? I would like for this to start making its way
upstream if there are no strong objections to the concept. After a
release or two, I'd like to start enabling it on more platforms.

Bart

Re: [PATCH v3 00/10] gpio: improve support for shared GPIOs

[Linus Walleij]

On Mon, Nov 10, 2025 at 10:46 AM Bartosz Golaszewski <brgl@bgdev.pl> wrote:

> Can I get some Reviewed-bys under the GPIO patches if there are no
> other open issues? I would like for this to start making its way
> upstream if there are no strong objections to the concept. After a
> release or two, I'd like to start enabling it on more platforms.

I'm convinced of the soundness of the general approach so I have
added R-B on the gpiolib patches, FWIW, for the rest:
Acked-by: Linus Walleij <linus.walleij@linaro.org>

You clearly have an idea and a plan here, and it looks solid to me.

Yours,
Linus Walleij