linux-kernel - Re: [PATCH 1/2] Documentation: ABI: Add sysfs-class-reboot-mode-reboot

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Message-ID: <1ddb483e-3c09-ff45-9d36-cf29a40ba55d@oss.qualcomm.com>
Date: Tue, 18 Nov 2025 22:07:51 +0530
From: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
To: Bjorn Andersson <andersson@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Sebastian Reichel <sre@...nel.org>,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-pm@...r.kernel.org,
        Sebastian Reichel <sebastian.reichel@...labora.com>
Subject: Re: [PATCH 1/2] Documentation: ABI: Add
 sysfs-class-reboot-mode-reboot_modes



On 11/18/2025 2:18 AM, Bjorn Andersson wrote:
> On Sun, Nov 16, 2025 at 07:44:24PM +0200, Dmitry Baryshkov wrote:
>> On Sun, Nov 16, 2025 at 08:49:47PM +0530, Shivendra Pratap wrote:
>>> Add ABI documentation for /sys/class/reboot-mode/*/reboot_modes, a
>>> read-only sysfs attribute exposing the list of supported reboot-mode
>>> arguments. This file is created by reboot-mode framework and provides a
>>> user-readable interface to query available reboot-mode arguments.
>>>
>>> Reviewed-by: Sebastian Reichel <sebastian.reichel@...labora.com>
>>> Signed-off-by: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
>>> ---
>>>  .../testing/sysfs-class-reboot-mode-reboot_modes   | 39 ++++++++++++++++++++++
>>>  1 file changed, 39 insertions(+)
>>>
>>> diff --git a/Documentation/ABI/testing/sysfs-class-reboot-mode-reboot_modes b/Documentation/ABI/testing/sysfs-class-reboot-mode-reboot_modes
>>> new file mode 100644
>>> index 0000000000000000000000000000000000000000..28280ffe9bf962ef9d2136ea5d7c6aef77c4bd34
>>> --- /dev/null
>>> +++ b/Documentation/ABI/testing/sysfs-class-reboot-mode-reboot_modes
>>> @@ -0,0 +1,39 @@
>>> +What:		/sys/class/reboot-mode/<driver>/reboot_modes
>>> +Date:		November 2025
>>> +KernelVersion:	6.18.0-rc5
>>> +Contact:	linux-pm@...r.kernel.org
>>> +		Description:
>>> +		This interface exposes the reboot-mode arguments
>>> +		registered with the reboot-mode framework. It is
>>> +		a read-only interface and provides a space
>>> +		separated list of reboot-mode arguments supported
>>> +		on the current platform.
>>> +		Example:
>>> +		 recovery fastboot bootloader
>>> +
>>> +		The exact sysfs path may vary depending on the
>>> +		name of the driver that registers the arguments.
>>> +		Example:
>>> +		 /sys/class/reboot-mode/nvmem-reboot-mode/reboot_modes
>>> +		 /sys/class/reboot-mode/syscon-reboot-mode/reboot_modes
>>> +		 /sys/class/reboot-mode/qcom-pon/reboot_modes
>>
>> This part is obvious, isn't it?
>>
>>> +
>>> +		The supported arguments can be used by userspace
>>> +		to invoke device reset using the reboot() system
>>> +		call, with the "argument" as string to "*arg"
>>> +		parameter along with LINUX_REBOOT_CMD_RESTART2.
>>> +		Example:
>>> +		 reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
>>> +		        LINUX_REBOOT_CMD_RESTART2, "bootloader");
>>
>> So, does one need to write a tool for invoking reboot with the corerct
>> set of args?
> 
> Here's an implementation of such tool
> https://github.com/systemd/systemd/blob/main/src/shared/reboot-util.c#L80

Should i include this link for an example of existing tools or i just add
add a line saying that such tools are already available?

> 
> Many other implementations of reboot provides the same.
> 
>> If we are adding a sysfs interface, wouldn't it be logical
>> to also add another sysfs file, setting the argument?
>>
> 
> The inclusion of the example indicates that we need to expose it in an
> accessible form, but I don't think we should, as it's already a
> widespread standard interface.
> 
> As such, I don't think the example adds any value, but it would be
> valuable to clarify that this is a standard interface.

ok. Will remove this example of reboot syscall and add a line to
indicate that this is standard interface.

thanks,
Shivendra