Message-Id: <20251130-next-15nov_expose_sysfs-v20-0-18c80f8248dd@oss.qualcomm.com>
Date: Sun, 30 Nov 2025 23:51:22 +0530
From: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
To: Sebastian Reichel <sre@...nel.org>,
        Bartosz Golaszewski <bgolasze@...cinc.com>,
        Bjorn Andersson <andersson@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-pm@...r.kernel.org, Bartosz Golaszewski <brgl@...ev.pl>,
        Shivendra Pratap <shivendra.pratap@....qualcomm.com>,
        Sebastian Reichel <sebastian.reichel@...labora.com>
Subject: [PATCH v20 0/2] reboot-mode: Expose sysfs for registered reboot
 modes

The reboot-mode framework provides infrastructure for drivers that want
to implement a userspace reboot command interface. However, there is
currently no standardized way for userspace to discover the list of
supported commands at runtime. This series introduces a sysfs interface
in the reboot-mode framework to expose the list of supported reboot-mode
commands to userspace. This will enable userspace tools to query
available reboot modes using the sysfs interface.

Example:
  cat /sys/class/reboot-mode/<driver-name>/reboot_modes

The series consists of two patches:
  1. power: reset: reboot-mode: Expose sysfs for registered reboot_modes
  2. Documentation: ABI: Add sysfs-class-reboot-mode-reboot_modes

These patches were previously being reviewed as part of “vendor resets
for PSCI SYSTEM_RESET2”, until v17. Following the suggestions from
Bjorn, the reboot-mode sysfs patches have been split into a separate
series here, for focused discussions and better alignment.

Previous discussion on these patches:
https://lore.kernel.org/all/20251109-arm-psci-system_reset2-vendor-reboots-v17-5-46e085bca4cc@oss.qualcomm.com/
https://lore.kernel.org/all/20251109-arm-psci-system_reset2-vendor-reboots-v17-4-46e085bca4cc@oss.qualcomm.com/

Signed-off-by: Shivendra Pratap <shivendra.pratap@....qualcomm.com>

Changes in v20:
By Bart
 - Use device_is_registered() instead of maintaining an explicit variable
   for status of device_register.
 - class_unregister already maintains an internal check; remove explicit
   check on status of class_register.
 - Protect the reboot_mode_list with mutex lock in reboot_modes_show.
 - Remove explicit "#ifdef MODULE"; subsys_initcall is just fine.

For Alignment
 - Move reboot_mode_register_device after the reboot_mode list additions
   are completed in reboot_mode_register. This also avoids explicit
   device_unregister in error paths and need for a lock in addition.
 - reboot-mode list protected in reboot_mode_unregister against a lock
   in reboot_modes_show.
 - Unregister reboot_mode_device before deleting the list in
   reboot_mode_unregister.
 - Although, we want to continue irrespective of the status of reboot_mode
   device_register, add a check and pr_debug to avoid compiler warning. 
- Link to v19: https://lore.kernel.org/r/20251122-next-15nov_expose_sysfs-v19-0-4d3d578ad9ee@oss.qualcomm.com

Changes in v19:
By Bart
 - Added subsys_initcall and moved class_register to initcall.

By Bjorn
 - Remove example of reboot SYSCALL from ABI documentation and mention
  about this being standard interface.

For Alignment
 - Added module_init/module_exit, in case reboot-mode is compiled as module.
 - Call class_unregister on module_exit.
 - Remove mutex lock on class_register as its not needed now.
 - Added a static bool reboot_mode_class_registered, to save the status of
   class registration.
 - Rename reboot_mode_create_device to reboot_mode_register_device.
    - Removed class_register as its moved to initcall.
 - Version correction for split series: Previous changed to v18.
 - Corrected Typo in Bjorn's Name in last change history.
- Link to v18: https://lore.kernel.org/r/20251116-next-15nov_expose_sysfs-v1-0-3b7880e5b40e@oss.qualcomm.com
  - *v18 was sent as v1 in last post.

Changes in v18:
By Bjorn
 - class is made static const and moved on the stack and registered
   using class_register.
 - Renamed name of class variable from rb_class to reboot_mode_class –
   Bart/ Bjorn
 - Renamed function name to prefix reboot_mode* to better align naming
   convention in reboot-mode.
 - Changed reboot_mode_device as static in reboot struct and registered
   using device_register.
 - Used dev_groups, instead of creating the sysfs attr file manually.
 - Continued the reboot-mode registration even if the sysfs creation
   fails at reboot_mode_create_device.
 - Used container of dev in show_reboot_modes to get the structure
   pointer of reboot.

By Bart
 -Synchronize class registration, as there may be race in this lazy
class_register.
 -Remove inversion kind of logic and align the return path of
show_reboot_modes

Other changes
 - reboot_dev is renamed to reboot_mode_device to align the naming
   conventions.
 - Keep a check on status of device_register with bool flag as
   device_unregister should be called only if the registration was
  successful.
 - Add a dummy function reboot_mode_device_release to avoid warn in
   driver unload path.
 - Date and version change in ABI documentation.
Link to v17:
https://lore.kernel.org/all/20251109-arm-psci-system_reset2-vendor-reboots-v17-0-46e085bca4cc@oss.qualcomm.com

---
To: Sebastian Reichel <sre@...nel.org>
Cc: linux-kernel@...r.kernel.org
Cc: linux-pm@...r.kernel.org

---
Shivendra Pratap (2):
      Documentation: ABI: Add sysfs-class-reboot-mode-reboot_modes
      power: reset: reboot-mode: Expose sysfs for registered reboot_modes

 .../testing/sysfs-class-reboot-mode-reboot_modes   | 36 ++++++++++
 drivers/power/reset/reboot-mode.c                  | 76 +++++++++++++++++++++-
 include/linux/reboot-mode.h                        |  6 ++
 3 files changed, 116 insertions(+), 2 deletions(-)
---
base-commit: 7d31f578f3230f3b7b33b0930b08f9afd8429817
change-id: 20251116-next-15nov_expose_sysfs-c0dbcf0d59da

Best regards,
-- 
Shivendra Pratap <shivendra.pratap@....qualcomm.com>

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