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

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Message-ID: <8fb6e8e0-cdca-0bd5-d0fe-56b5f6d27a5c@oss.qualcomm.com>
Date: Sat, 18 Oct 2025 01:10:09 +0530
From: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
To: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Cc: Bjorn Andersson <andersson@...nel.org>,
        Sebastian Reichel
 <sre@...nel.org>, Rob Herring <robh@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Souvik Chakravarty <Souvik.Chakravarty@....com>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>,
        Andy Yan <andy.yan@...k-chips.com>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Konrad Dybcio <konradybcio@...nel.org>,
        cros-qcom-dts-watchers@...omium.org, Vinod Koul <vkoul@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Florian Fainelli <florian.fainelli@...adcom.com>,
        John Stultz <john.stultz@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Mukesh Ojha <mukesh.ojha@....qualcomm.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Andre Draszik
 <andre.draszik@...aro.org>,
        Kathiravan Thirumoorthy <kathiravan.thirumoorthy@....qualcomm.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org,
        Elliot Berman <quic_eberman@...cinc.com>,
        Srinivas Kandagatla <srini@...nel.org>
Subject: Re: [PATCH v16 05/14] power: reset: reboot-mode: Expose sysfs for
 registered reboot_modes



On 10/15/2025 8:17 PM, Bartosz Golaszewski wrote:
> On Wed, 15 Oct 2025 at 06:39, Shivendra Pratap
> <shivendra.pratap@....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@....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