[PATCH v19 2/2] power: reset: reboot-mode: Expose sysfs for registered reboot_modes

[Shivendra Pratap <shivendra.pratap@oss.qualcomm.com>]

Currently, there is no standardized mechanism for userspace to discover
which reboot-modes are supported on a given platform. This limitation
forces tools and scripts to rely on hardcoded assumptions about the
supported reboot-modes.

Create a class 'reboot-mode' and a device under it to expose a sysfs
interface to show the available reboot mode arguments to userspace. Use
the driver_name field of the struct reboot_mode_driver to create the
device.  For device-based drivers, configure the device driver name as
driver_name.

This results in the creation of:
  /sys/class/reboot-mode/<driver>/reboot_modes

This read-only sysfs file will exposes the list of supported reboot
modes arguments provided by the driver, enabling userspace to query the
list of arguments.

Signed-off-by: Shivendra Pratap <shivendra.pratap@oss.qualcomm.com>
---
 drivers/power/reset/reboot-mode.c | 86 +++++++++++++++++++++++++++++++++++++++
 include/linux/reboot-mode.h       |  3 ++
 2 files changed, 89 insertions(+)

diff --git a/drivers/power/reset/reboot-mode.c b/drivers/power/reset/reboot-mode.c
index fba53f638da04655e756b5f8b7d2d666d1379535..71cd97ffb3ee8da530514ab918bc6d58a122b4ce 100644
--- a/drivers/power/reset/reboot-mode.c
+++ b/drivers/power/reset/reboot-mode.c
@@ -13,12 +13,61 @@
 
 #define PREFIX "mode-"
 
+static bool reboot_mode_class_registered;
+
 struct mode_info {
 	const char *mode;
 	u32 magic;
 	struct list_head list;
 };
 
+static ssize_t reboot_modes_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct reboot_mode_driver *reboot;
+	struct mode_info *info;
+	ssize_t size = 0;
+
+	reboot = container_of(dev, struct reboot_mode_driver, reboot_mode_device);
+	if (!reboot)
+		return -ENODATA;
+
+	list_for_each_entry(info, &reboot->head, list)
+		size += sysfs_emit_at(buf, size, "%s ", info->mode);
+
+	if (!size)
+		return -ENODATA;
+
+	return size + sysfs_emit_at(buf, size - 1, "\n");
+}
+static DEVICE_ATTR_RO(reboot_modes);
+
+static struct attribute *reboot_mode_attrs[] = {
+	&dev_attr_reboot_modes.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(reboot_mode);
+
+static const struct class reboot_mode_class = {
+	.name = "reboot-mode",
+	.dev_groups = reboot_mode_groups,
+};
+
+static void reboot_mode_device_release(struct device *dev)
+{
+    /* place holder to avoid warning on device_unregister. nothing to free */
+}
+
+static void reboot_mode_register_device(struct reboot_mode_driver *reboot)
+{
+	reboot->reboot_mode_device.class = &reboot_mode_class;
+	reboot->reboot_mode_device.release = reboot_mode_device_release;
+	dev_set_name(&reboot->reboot_mode_device, reboot->driver_name);
+	if (!device_register(&reboot->reboot_mode_device))
+		reboot->reboot_mode_device_registered = true;
+	else
+		reboot->reboot_mode_device_registered = false;
+}
+
 static unsigned int get_reboot_mode_magic(struct reboot_mode_driver *reboot,
 					  const char *cmd)
 {
@@ -78,6 +127,9 @@ int reboot_mode_register(struct reboot_mode_driver *reboot)
 
 	INIT_LIST_HEAD(&reboot->head);
 
+	if (reboot_mode_class_registered)
+		reboot_mode_register_device(reboot);
+
 	for_each_property_of_node(np, prop) {
 		if (strncmp(prop->name, PREFIX, len))
 			continue;
@@ -119,6 +171,11 @@ int reboot_mode_register(struct reboot_mode_driver *reboot)
 	list_for_each_entry(info, &reboot->head, list)
 		kfree_const(info->mode);
 
+	if (reboot->reboot_mode_device_registered) {
+		device_unregister(&reboot->reboot_mode_device);
+		reboot->reboot_mode_device_registered = false;
+	}
+
 	return ret;
 }
 EXPORT_SYMBOL_GPL(reboot_mode_register);
@@ -136,6 +193,11 @@ int reboot_mode_unregister(struct reboot_mode_driver *reboot)
 	list_for_each_entry(info, &reboot->head, list)
 		kfree_const(info->mode);
 
+	if (reboot->reboot_mode_device_registered) {
+		device_unregister(&reboot->reboot_mode_device);
+		reboot->reboot_mode_device_registered = false;
+	}
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(reboot_mode_unregister);
@@ -162,6 +224,7 @@ int devm_reboot_mode_register(struct device *dev,
 	if (!dr)
 		return -ENOMEM;
 
+	reboot->driver_name = reboot->dev->driver->name;
 	rc = reboot_mode_register(reboot);
 	if (rc) {
 		devres_free(dr);
@@ -199,6 +262,29 @@ void devm_reboot_mode_unregister(struct device *dev,
 }
 EXPORT_SYMBOL_GPL(devm_reboot_mode_unregister);
 
+static int __init reboot_mode_init(void)
+{
+	if (class_register(&reboot_mode_class))
+		reboot_mode_class_registered = false;
+	else
+		reboot_mode_class_registered = true;
+
+	return 0;
+}
+
+static void __exit reboot_mode_exit(void)
+{
+	if (reboot_mode_class_registered)
+		class_unregister(&reboot_mode_class);
+}
+
+#ifdef MODULE
+module_init(reboot_mode_init);
+module_exit(reboot_mode_exit);
+#else
+subsys_initcall(reboot_mode_init);
+#endif
+
 MODULE_AUTHOR("Andy Yan <andy.yan@rock-chips.com>");
 MODULE_DESCRIPTION("System reboot mode core library");
 MODULE_LICENSE("GPL v2");
diff --git a/include/linux/reboot-mode.h b/include/linux/reboot-mode.h
index 4a2abb38d1d612ec0fdf05eb18c98b210f631b7f..400cfde0e029aef14ff90a11b9d12d0c3ce8dee6 100644
--- a/include/linux/reboot-mode.h
+++ b/include/linux/reboot-mode.h
@@ -5,6 +5,9 @@
 struct reboot_mode_driver {
 	struct device *dev;
 	struct list_head head;
+	const char *driver_name;
+	struct device reboot_mode_device;
+	bool reboot_mode_device_registered;
 	int (*write)(struct reboot_mode_driver *reboot, unsigned int magic);
 	struct notifier_block reboot_notifier;
 };

-- 
2.34.1