Re: [PATCH v14 05/10] power: reset: reboot-mode: Expose sysfs for registered reboot_modes

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

On 9/17/2025 12:32 AM, Sebastian Reichel wrote:
> Hi,
> 
> On Fri, Aug 15, 2025 at 08:05:10PM +0530, Shivendra Pratap wrote:
>> 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.
>>
>> Provision the register function with an additional parameter to
>> get an explicit driver_name. Create the device using this
>> driver_name. For platform drivers, use the driver_name configured
>> in dev node.
>>
>> 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.
>>
>> Align the clean up path to maintain backward compatibility for
>> existing reboot-mode based drivers.
>>
>> Signed-off-by: Shivendra Pratap <shivendra.pratap@oss.qualcomm.com>
>> ---
>>  drivers/power/reset/reboot-mode.c | 131 +++++++++++++++++++++++++++++++-------
>>  include/linux/reboot-mode.h       |   4 +-
>>  2 files changed, 110 insertions(+), 25 deletions(-)
>>
>> diff --git a/drivers/power/reset/reboot-mode.c b/drivers/power/reset/reboot-mode.c
>> index ac81b8b0a9b7fc31f8ef21024333a050087ce90f..7ecab050e496af3e1cc01c1a4614787707cb74b4 100644
>> --- a/drivers/power/reset/reboot-mode.c
>> +++ b/drivers/power/reset/reboot-mode.c
>> @@ -6,6 +6,7 @@
>>  #define pr_fmt(fmt)	"reboot-mode: " fmt
>>  
>>  #include <linux/device.h>
>> +#include <linux/err.h>
>>  #include <linux/init.h>
>>  #include <linux/kernel.h>
>>  #include <linux/list.h>
>> @@ -23,6 +24,8 @@ struct mode_info {
>>  	struct list_head list;
>>  };
>>  
>> +static struct class *rb_class;
>> +
>>  static u64 get_reboot_mode_magic(struct reboot_mode_driver *reboot, const char *cmd)
>>  {
>>  	const char *normal = "normal";
>> @@ -75,26 +78,121 @@ static int reboot_mode_notify(struct notifier_block *this,
>>  	return NOTIFY_DONE;
>>  }
>>  
>> +static void release_reboot_mode_device(struct device *dev, void *res);
>> +
>> +static ssize_t reboot_modes_show(struct device *dev, struct device_attribute *attr, char *buf)
>> +{
>> +	struct reboot_mode_driver **devres_reboot;
>> +	struct reboot_mode_driver *reboot;
>> +	struct mode_info *info;
>> +	ssize_t size = 0;
>> +
>> +	devres_reboot = devres_find(dev, release_reboot_mode_device, NULL, NULL);
>> +	if (!devres_reboot || !(*devres_reboot))
>> +		return -ENODATA;
>> +
>> +	reboot = *devres_reboot;
>> +	mutex_lock(&reboot->rb_lock);
>> +	list_for_each_entry(info, &reboot->head, list) {
>> +		size += sprintf(buf + size, "%s ", info->mode);
> 
> sysfs_emit_at

ACK. will update.

> 
>> +	}
>> +	mutex_unlock(&reboot->rb_lock);
>> +
>> +	if (size) {
>> +		size += sprintf(buf + size - 1, "\n");
> 
> sysfs_emit_at

ACK. will update.

> 
>> +		return size;
>> +	}
>> +
>> +	return -ENODATA;
>> +}
>> +static DEVICE_ATTR_RO(reboot_modes);
>> +
>> +static void release_reboot_mode_device(struct device *dev, void *res)
>> +{
>> +	struct reboot_mode_driver *reboot = *(struct reboot_mode_driver **)res;
>> +	struct mode_info *info;
>> +	struct mode_info *next;
>> +
>> +	unregister_reboot_notifier(&reboot->reboot_notifier);
>> +
>> +	mutex_lock(&reboot->rb_lock);
>> +	list_for_each_entry_safe(info, next, &reboot->head, list) {
>> +		list_del(&info->list);
>> +		kfree_const(info->mode);
>> +		kfree(info);
>> +	}
>> +	mutex_unlock(&reboot->rb_lock);
>> +
>> +	device_remove_file(reboot->reboot_dev, &dev_attr_reboot_modes);
>> +}
>> +
>> +static int create_reboot_mode_device(struct reboot_mode_driver *reboot,
>> +				     const char *dev_name)
> 
> Instead of adding more and more arguments to this, just add a name
> field to struct reboot_mode_driver.

ACK. will update.

thanks,
Shivendra