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

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Message-ID: <yxy7b4pdv4o7dvfjndi5awg5tcobkzwuewn6sal2v2eydv4aes@wkaknlotycrk>
Date: Tue, 18 Nov 2025 21:22:46 -0600
From: Bjorn Andersson <andersson@...nel.org>
To: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
Cc: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>, 
	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 Tue, Nov 18, 2025 at 10:07:51PM +0530, Shivendra Pratap wrote:
> 
> 
> 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.
> 

This sounds good to me.

Thanks,
Bjorn

> thanks,
> Shivendra