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Message-Id: <20251116-next-15nov_expose_sysfs-v1-2-3b7880e5b40e@oss.qualcomm.com>
Date: Sun, 16 Nov 2025 20:49:48 +0530
From: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
To: Sebastian Reichel <sre@...nel.org>,
Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
Bjorn Andersson <andersson@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
linux-pm@...r.kernel.org,
Shivendra Pratap <shivendra.pratap@....qualcomm.com>
Subject: [PATCH 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 | 72 +++++++++++++++++++++++++++++++++++++++
include/linux/reboot-mode.h | 3 ++
2 files changed, 75 insertions(+)
diff --git a/drivers/power/reset/reboot-mode.c b/drivers/power/reset/reboot-mode.c
index fba53f638da04655e756b5f8b7d2d666d1379535..062df67735c4818cfeb894941e537f19ea9d4ccb 100644
--- a/drivers/power/reset/reboot-mode.c
+++ b/drivers/power/reset/reboot-mode.c
@@ -7,18 +7,77 @@
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
+#include <linux/mutex.h>
#include <linux/of.h>
#include <linux/reboot.h>
#include <linux/reboot-mode.h>
#define PREFIX "mode-"
+static DEFINE_MUTEX(reboot_mode_mutex);
+
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_create_device(struct reboot_mode_driver *reboot)
+{
+ static bool is_class_registered;
+
+ reboot->reboot_mode_device_registered = false;
+
+ scoped_guard(mutex, &reboot_mode_mutex) {
+ if (!is_class_registered) {
+ if (!class_register(&reboot_mode_class))
+ is_class_registered = true;
+ }
+ }
+
+ 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;
+}
+
static unsigned int get_reboot_mode_magic(struct reboot_mode_driver *reboot,
const char *cmd)
{
@@ -78,6 +137,8 @@ int reboot_mode_register(struct reboot_mode_driver *reboot)
INIT_LIST_HEAD(&reboot->head);
+ reboot_mode_create_device(reboot);
+
for_each_property_of_node(np, prop) {
if (strncmp(prop->name, PREFIX, len))
continue;
@@ -119,6 +180,11 @@ 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 +202,11 @@ 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 +233,7 @@ 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);
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
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