[PATCH v16 05/14] power: reset: reboot-mode: Expose sysfs for registered reboot_modes

[Shivendra Pratap]

On 10/15/2025 8:17 PM, Bartosz Golaszewski wrote:
> On Wed, 15 Oct 2025 at 06:39, Shivendra Pratap
> <shivendra.pratap at oss.qualcomm.com> 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. 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.
>>
>> Align the clean up path to maintain backward compatibility for
>> existing reboot-mode based drivers.
>>
>> Signed-off-by: Shivendra Pratap <shivendra.pratap at oss.qualcomm.com>
> 
> [snip]
> 
>> +
>> +static int create_reboot_mode_device(struct reboot_mode_driver *reboot)
>> +{
>> +       struct reboot_mode_driver **dr;
>> +       int ret = 0;
>> +
>> +       if (!rb_class) {
>> +               rb_class = class_create("reboot-mode");
>> +               if (IS_ERR(rb_class))
>> +                       return PTR_ERR(rb_class);
>> +       }
>> +
>> +       reboot->reboot_dev = device_create(rb_class, NULL, 0, NULL, reboot->driver_name);
>> +       if (IS_ERR(reboot->reboot_dev))
>> +               return PTR_ERR(reboot->reboot_dev);
>> +
>> +       ret = device_create_file(reboot->reboot_dev, &dev_attr_reboot_modes);
>> +       if (ret)
>> +               goto create_file_err;
>> +
>> +       dr = devres_alloc(release_reboot_mode_device, sizeof(*dr), GFP_KERNEL);
>> +       if (!dr) {
>> +               ret = -ENOMEM;
>> +               goto devres_alloc_error;
>> +       }
>> +
>> +       *dr = reboot;
>> +       devres_add(reboot->reboot_dev, dr);
> 
> If you're using devres here - at least make it obvious by adding the
> devm_ prefix to the function name and make it take an explicit struct
> device * parameter so that it's clear who owns the managed resource.
> 

sure. we can add devm_ prefix to the function name.
reboot->reboot_dev is an internal member of struct reboot_mode_driver *reboot.
The struct reboot_mode_driver *reboot is owned by the calling driver.
If we want to PASS reboot->reboot_dev to the devm_ prefixed function call, we
will need to kind of split create_reboot_mode_device into two calls - device_create
in a separate function and then call the devm_ prefix function where we add the devres_alloc.
Can you suggest a bit more on this?

thanks,
Shivendra