gpio: introduce utilities for synchronous fake device creation

Both gpio-sim and gpio-virtuser share a mechanism to instantiate a
platform device, wait for probe completion, and retrieve the probe
success or error status synchronously. With gpio-aggregator planned to
adopt this approach for its configfs interface, it's time to factor
out the common code.

Add dev-sync-probe.[ch] to house helper functions used by all such
implementations.

No functional change.

Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
Link: https://lore.kernel.org/r/20250221133501.2203897-2-koichiro.den@canonical.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index f518f54584461aa47e8f56e7a6781f091f319415..d6ac1a01c636c8bdbd35bf4cbda313aee0a485f7 100644 (file)
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -1948,3 +1948,6 @@ config GPIO_VIRTUSER
 endmenu
 
 endif
+
+config DEV_SYNC_PROBE
+       tristate

diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index af3ba4d81b583842893ea69e677fbe2abf31bc7b..af130882ffeeef8b1d518867bfe1493ec4f21b5f 100644 (file)
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -19,6 +19,9 @@ obj-$(CONFIG_GPIO_GENERIC)    += gpio-generic.o
 # directly supported by gpio-generic
 gpio-generic-$(CONFIG_GPIO_GENERIC)    += gpio-mmio.o
 
+# Utilities for drivers that need synchronous fake device creation
+obj-$(CONFIG_DEV_SYNC_PROBE)           += dev-sync-probe.o
+
 obj-$(CONFIG_GPIO_104_DIO_48E)         += gpio-104-dio-48e.o
 obj-$(CONFIG_GPIO_104_IDI_48)          += gpio-104-idi-48.o
 obj-$(CONFIG_GPIO_104_IDIO_16)         += gpio-104-idio-16.o

diff --git a/drivers/gpio/dev-sync-probe.c b/drivers/gpio/dev-sync-probe.c
new file mode 100644 (file)
index 0000000..9ea733b
--- /dev/null
+++ b/drivers/gpio/dev-sync-probe.c
@@ -0,0 +1,97 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Common code for drivers creating fake platform devices.
+ *
+ * Provides synchronous device creation: waits for probe completion and
+ * returns the probe success or error status to the device creator.
+ *
+ * Copyright (C) 2021 Bartosz Golaszewski <brgl@bgdev.pl>
+ * Copyright (C) 2025 Koichiro Den <koichiro.den@canonical.com>
+ */
+
+#include <linux/device.h>
+#include <linux/slab.h>
+
+#include "dev-sync-probe.h"
+
+static int dev_sync_probe_notifier_call(struct notifier_block *nb,
+                                       unsigned long action, void *data)
+{
+       struct dev_sync_probe_data *pdata;
+       struct device *dev = data;
+
+       pdata = container_of(nb, struct dev_sync_probe_data, bus_notifier);
+       if (!device_match_name(dev, pdata->name))
+               return NOTIFY_DONE;
+
+       switch (action) {
+       case BUS_NOTIFY_BOUND_DRIVER:
+               pdata->driver_bound = true;
+               break;
+       case BUS_NOTIFY_DRIVER_NOT_BOUND:
+               pdata->driver_bound = false;
+               break;
+       default:
+               return NOTIFY_DONE;
+       }
+
+       complete(&pdata->probe_completion);
+       return NOTIFY_OK;
+}
+
+void dev_sync_probe_init(struct dev_sync_probe_data *data)
+{
+       memset(data, 0, sizeof(*data));
+       init_completion(&data->probe_completion);
+       data->bus_notifier.notifier_call = dev_sync_probe_notifier_call;
+}
+EXPORT_SYMBOL_GPL(dev_sync_probe_init);
+
+int dev_sync_probe_register(struct dev_sync_probe_data *data,
+                           struct platform_device_info *pdevinfo)
+{
+       struct platform_device *pdev;
+       char *name;
+
+       name = kasprintf(GFP_KERNEL, "%s.%d", pdevinfo->name, pdevinfo->id);
+       if (!name)
+               return -ENOMEM;
+
+       data->driver_bound = false;
+       data->name = name;
+       reinit_completion(&data->probe_completion);
+       bus_register_notifier(&platform_bus_type, &data->bus_notifier);
+
+       pdev = platform_device_register_full(pdevinfo);
+       if (IS_ERR(pdev)) {
+               bus_unregister_notifier(&platform_bus_type, &data->bus_notifier);
+               kfree(data->name);
+               return PTR_ERR(pdev);
+       }
+
+       wait_for_completion(&data->probe_completion);
+       bus_unregister_notifier(&platform_bus_type, &data->bus_notifier);
+
+       if (!data->driver_bound) {
+               platform_device_unregister(pdev);
+               kfree(data->name);
+               return -ENXIO;
+       }
+
+       data->pdev = pdev;
+       return 0;
+}
+EXPORT_SYMBOL_GPL(dev_sync_probe_register);
+
+void dev_sync_probe_unregister(struct dev_sync_probe_data *data)
+{
+       platform_device_unregister(data->pdev);
+       kfree(data->name);
+       data->pdev = NULL;
+}
+EXPORT_SYMBOL_GPL(dev_sync_probe_unregister);
+
+MODULE_AUTHOR("Bartosz Golaszewski <brgl@bgdev.pl>");
+MODULE_AUTHOR("Koichiro Den <koichiro.den@canonical.com>");
+MODULE_DESCRIPTION("Utilities for synchronous fake device creation");
+MODULE_LICENSE("GPL");

diff --git a/drivers/gpio/dev-sync-probe.h b/drivers/gpio/dev-sync-probe.h
new file mode 100644 (file)
index 0000000..4b3d52b
--- /dev/null
+++ b/drivers/gpio/dev-sync-probe.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef DEV_SYNC_PROBE_H
+#define DEV_SYNC_PROBE_H
+
+#include <linux/completion.h>
+#include <linux/notifier.h>
+#include <linux/platform_device.h>
+
+struct dev_sync_probe_data {
+       struct platform_device *pdev;
+       const char *name;
+
+       /* Synchronize with probe */
+       struct notifier_block bus_notifier;
+       struct completion probe_completion;
+       bool driver_bound;
+};
+
+void dev_sync_probe_init(struct dev_sync_probe_data *data);
+int dev_sync_probe_register(struct dev_sync_probe_data *data,
+                           struct platform_device_info *pdevinfo);
+void dev_sync_probe_unregister(struct dev_sync_probe_data *data);
+
+#endif /* DEV_SYNC_PROBE_H */