[PATCH 1/3] gpio: pseudo: common helper functions for pseudo gpio devices

[Koichiro Den <koichiro.den@xxxxxxxxxxxxx>]

Both gpio-sim and gpio-virtuser share a mechanism to instantiate a
platform device and wait synchronously for probe completion.
With gpio-aggregator adopting the same approach in a later commit for
its configfs interface, it's time to factor out the common code.

Add gpio-pseudo.[ch] to house helper functions used by all the pseudo
GPIO device implementations.

No functional change.

Signed-off-by: Koichiro Den <koichiro.den@xxxxxxxxxxxxx>
---
 drivers/gpio/Kconfig       |  4 ++
 drivers/gpio/Makefile      |  1 +
 drivers/gpio/gpio-pseudo.c | 86 ++++++++++++++++++++++++++++++++++++++
 drivers/gpio/gpio-pseudo.h | 24 +++++++++++
 4 files changed, 115 insertions(+)
 create mode 100644 drivers/gpio/gpio-pseudo.c
 create mode 100644 drivers/gpio/gpio-pseudo.h

diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 56c1f30ac195..1e2c95e03a95 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -1863,6 +1863,10 @@ config GPIO_MPSSE
 
 endmenu
 
+# This symbol is selected by some pseudo gpio device implementations
+config GPIO_PSEUDO
+	bool
+
 menu "Virtual GPIO drivers"
 
 config GPIO_AGGREGATOR
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index af3ba4d81b58..5eb54147a1ab 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -136,6 +136,7 @@ obj-$(CONFIG_GPIO_PISOSR)		+= gpio-pisosr.o
 obj-$(CONFIG_GPIO_PL061)		+= gpio-pl061.o
 obj-$(CONFIG_GPIO_PMIC_EIC_SPRD)	+= gpio-pmic-eic-sprd.o
 obj-$(CONFIG_GPIO_POLARFIRE_SOC)	+= gpio-mpfs.o
+obj-$(CONFIG_GPIO_PSEUDO)		+= gpio-pseudo.o
 obj-$(CONFIG_GPIO_PXA)			+= gpio-pxa.o
 obj-$(CONFIG_GPIO_RASPBERRYPI_EXP)	+= gpio-raspberrypi-exp.o
 obj-$(CONFIG_GPIO_RC5T583)		+= gpio-rc5t583.o
diff --git a/drivers/gpio/gpio-pseudo.c b/drivers/gpio/gpio-pseudo.c
new file mode 100644
index 000000000000..6e3da05440d8
--- /dev/null
+++ b/drivers/gpio/gpio-pseudo.c
@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Helper functions for Pseudo GPIOs
+ *
+ * Copyright 2025 Canonical Ltd.
+ */
+
+#include "gpio-pseudo.h"
+
+static int pseudo_gpio_notifier_call(struct notifier_block *nb,
+				     unsigned long action,
+				     void *data)
+{
+	struct pseudo_gpio_common *common;
+	struct device *dev = data;
+
+	common = container_of(nb, struct pseudo_gpio_common, bus_notifier);
+	if (!device_match_name(dev, common->name))
+		return NOTIFY_DONE;
+
+	switch (action) {
+	case BUS_NOTIFY_BOUND_DRIVER:
+		common->driver_bound = true;
+		break;
+	case BUS_NOTIFY_DRIVER_NOT_BOUND:
+		common->driver_bound = false;
+		break;
+	default:
+		return NOTIFY_DONE;
+	}
+
+	complete(&common->probe_completion);
+	return NOTIFY_OK;
+}
+
+void pseudo_gpio_init(struct pseudo_gpio_common *common)
+{
+	memset(common, 0, sizeof(*common));
+	init_completion(&common->probe_completion);
+	common->bus_notifier.notifier_call = pseudo_gpio_notifier_call;
+}
+EXPORT_SYMBOL_GPL(pseudo_gpio_init);
+
+int pseudo_gpio_register(struct pseudo_gpio_common *common,
+			 struct platform_device_info *pdevinfo)
+{
+	struct platform_device *pdev;
+	char *name;
+
+	name = kasprintf(GFP_KERNEL, "%s.%u", pdevinfo->name, pdevinfo->id);
+	if (!name)
+		return -ENOMEM;
+
+	common->driver_bound = false;
+	common->name = name;
+	reinit_completion(&common->probe_completion);
+	bus_register_notifier(&platform_bus_type, &common->bus_notifier);
+
+	pdev = platform_device_register_full(pdevinfo);
+	if (IS_ERR(pdev)) {
+		bus_unregister_notifier(&platform_bus_type, &common->bus_notifier);
+		kfree(common->name);
+		return PTR_ERR(pdev);
+	}
+
+	wait_for_completion(&common->probe_completion);
+	bus_unregister_notifier(&platform_bus_type, &common->bus_notifier);
+
+	if (!common->driver_bound) {
+		platform_device_unregister(pdev);
+		kfree(common->name);
+		return -ENXIO;
+	}
+
+	common->pdev = pdev;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(pseudo_gpio_register);
+
+void pseudo_gpio_unregister(struct pseudo_gpio_common *common)
+{
+	platform_device_unregister(common->pdev);
+	kfree(common->name);
+	common->pdev = NULL;
+}
+EXPORT_SYMBOL_GPL(pseudo_gpio_unregister);
diff --git a/drivers/gpio/gpio-pseudo.h b/drivers/gpio/gpio-pseudo.h
new file mode 100644
index 000000000000..093112b6cce5
--- /dev/null
+++ b/drivers/gpio/gpio-pseudo.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef GPIO_PSEUDO_H
+#define GPIO_PSEUDO_H
+
+#include <linux/completion.h>
+#include <linux/platform_device.h>
+
+struct pseudo_gpio_common {
+	struct platform_device *pdev;
+	const char *name;
+
+	/* Synchronize with probe */
+	struct notifier_block bus_notifier;
+	struct completion probe_completion;
+	bool driver_bound;
+};
+
+void pseudo_gpio_init(struct pseudo_gpio_common *common);
+int pseudo_gpio_register(struct pseudo_gpio_common *common,
+			 struct platform_device_info *pdevinfo);
+void pseudo_gpio_unregister(struct pseudo_gpio_common *common);
+
+#endif /* GPIO_PSEUDO_H */
-- 
2.45.2