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Message-Id: <20251227-next-15nov_expose_sysfs-v22-2-2d153438ba19@oss.qualcomm.com>
Date: Sat, 27 Dec 2025 00:26:34 +0530
From: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
To: Sebastian Reichel <sre@...nel.org>,
Bartosz Golaszewski <bgolasze@...cinc.com>,
Bjorn Andersson <andersson@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
linux-pm@...r.kernel.org, Bartosz Golaszewski <brgl@...ev.pl>,
Shivendra Pratap <shivendra.pratap@....qualcomm.com>
Subject: [PATCH v22 2/2] power: reset: reboot-mode: Expose sysfs for
registered reboot_modes
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@....qualcomm.com>
---
drivers/power/reset/reboot-mode.c | 139 +++++++++++++++++++++++++++++++++++++-
include/linux/reboot-mode.h | 1 +
2 files changed, 137 insertions(+), 3 deletions(-)
diff --git a/drivers/power/reset/reboot-mode.c b/drivers/power/reset/reboot-mode.c
index fba53f638da04655e756b5f8b7d2d666d1379535..96d0201697a539c6d048dac021db97e4e3063366 100644
--- a/drivers/power/reset/reboot-mode.c
+++ b/drivers/power/reset/reboot-mode.c
@@ -6,10 +6,12 @@
#include <linux/device.h>
#include <linux/init.h>
#include <linux/kernel.h>
+#include <linux/list.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/reboot.h>
#include <linux/reboot-mode.h>
+#include <linux/slab.h>
#define PREFIX "mode-"
@@ -19,6 +21,42 @@ struct mode_info {
struct list_head list;
};
+struct sysfs_data {
+ const char *mode;
+ struct list_head list;
+};
+
+static ssize_t reboot_modes_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+ struct sysfs_data *sysfs_info;
+ struct list_head *head;
+ ssize_t size = 0;
+
+ head = dev_get_drvdata(dev);
+ if (!head)
+ return -ENODATA;
+
+ list_for_each_entry(sysfs_info, head, list)
+ size += sysfs_emit_at(buf, size, "%s ", sysfs_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 unsigned int get_reboot_mode_magic(struct reboot_mode_driver *reboot,
const char *cmd)
{
@@ -62,6 +100,61 @@ static int reboot_mode_notify(struct notifier_block *this,
return NOTIFY_DONE;
}
+static int reboot_mode_create_device(struct reboot_mode_driver *reboot)
+{
+ struct sysfs_data *sysfs_info;
+ struct sysfs_data *next;
+ struct list_head *head;
+ struct mode_info *info;
+ int ret;
+
+ head = kzalloc(sizeof(*head), GFP_KERNEL);
+ if (!head) {
+ ret = -ENOMEM;
+ goto error;
+ }
+
+ INIT_LIST_HEAD(head);
+
+ list_for_each_entry(info, &reboot->head, list) {
+ sysfs_info = kzalloc(sizeof(*sysfs_info), GFP_KERNEL);
+ if (!sysfs_info) {
+ ret = -ENOMEM;
+ goto error;
+ }
+
+ sysfs_info->mode = kstrdup_const(info->mode, GFP_KERNEL);
+ if (!sysfs_info->mode) {
+ kfree(sysfs_info);
+ ret = -ENOMEM;
+ goto error;
+ }
+
+ list_add_tail(&sysfs_info->list, head);
+ }
+
+ reboot->reboot_mode_device = device_create(&reboot_mode_class, NULL, 0,
+ (void *)head, reboot->dev->driver->name);
+
+ if (IS_ERR(reboot->reboot_mode_device)) {
+ ret = PTR_ERR(reboot->reboot_mode_device);
+ goto error;
+ }
+
+ return 0;
+
+error:
+ list_for_each_entry_safe(sysfs_info, next, head, list) {
+ list_del(&sysfs_info->list);
+ kfree_const(sysfs_info->mode);
+ kfree(sysfs_info);
+ }
+
+ kfree(head);
+ reboot->reboot_mode_device = NULL;
+ return ret;
+}
+
/**
* reboot_mode_register - register a reboot mode driver
* @reboot: reboot mode driver
@@ -113,16 +206,39 @@ int reboot_mode_register(struct reboot_mode_driver *reboot)
reboot->reboot_notifier.notifier_call = reboot_mode_notify;
register_reboot_notifier(&reboot->reboot_notifier);
+ ret = reboot_mode_create_device(reboot);
+ if (ret)
+ goto error;
+
return 0;
error:
- list_for_each_entry(info, &reboot->head, list)
- kfree_const(info->mode);
-
+ reboot_mode_unregister(reboot);
return ret;
}
EXPORT_SYMBOL_GPL(reboot_mode_register);
+static inline void reboot_mode_unregister_device(struct reboot_mode_driver *reboot)
+{
+ struct sysfs_data *sysfs_info;
+ struct sysfs_data *next;
+ struct list_head *head;
+
+ head = dev_get_drvdata(reboot->reboot_mode_device);
+ device_unregister(reboot->reboot_mode_device);
+ reboot->reboot_mode_device = NULL;
+
+ if (head) {
+ list_for_each_entry_safe(sysfs_info, next, head, list) {
+ list_del(&sysfs_info->list);
+ kfree_const(sysfs_info->mode);
+ kfree(sysfs_info);
+ }
+ }
+
+ kfree(head);
+}
+
/**
* reboot_mode_unregister - unregister a reboot mode driver
* @reboot: reboot mode driver
@@ -131,7 +247,11 @@ int reboot_mode_unregister(struct reboot_mode_driver *reboot)
{
struct mode_info *info;
+ if (!reboot->reboot_mode_device)
+ return -ENODEV;
+
unregister_reboot_notifier(&reboot->reboot_notifier);
+ reboot_mode_unregister_device(reboot);
list_for_each_entry(info, &reboot->head, list)
kfree_const(info->mode);
@@ -199,6 +319,19 @@ void devm_reboot_mode_unregister(struct device *dev,
}
EXPORT_SYMBOL_GPL(devm_reboot_mode_unregister);
+static int __init reboot_mode_init(void)
+{
+ return class_register(&reboot_mode_class);
+}
+
+static void __exit reboot_mode_exit(void)
+{
+ class_unregister(&reboot_mode_class);
+}
+
+subsys_initcall(reboot_mode_init);
+module_exit(reboot_mode_exit);
+
MODULE_AUTHOR("Andy Yan <andy.yan@...k-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..b56783c32068096325f92445b9530d1856c4826c 100644
--- a/include/linux/reboot-mode.h
+++ b/include/linux/reboot-mode.h
@@ -5,6 +5,7 @@
struct reboot_mode_driver {
struct device *dev;
struct list_head head;
+ struct device *reboot_mode_device;
int (*write)(struct reboot_mode_driver *reboot, unsigned int magic);
struct notifier_block reboot_notifier;
};
--
2.34.1
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