Subject: Re: [PATCH v3 00/25] Introduce power-off+restart call chain API

From: Dmitry Osipenko <[email-masked]>
Date: Mon, 8 Nov 2021 04:14:30 +0300

08.11.2021 03:44, Dmitry Osipenko пишет:
> Problem
> -------
> 
> SoC devices require power-off call chaining functionality from kernel.
> We have a widely used restart chaining provided by restart notifier API,
> but nothing for power-off.
> 
> Solution
> --------
> 
> Introduce new API that provides both restart and power-off call chains.
> 
> Why combine restart with power-off? Because drivers often do both.
> More practical to have API that provides both under the same roof.
> 
> The new API is designed with simplicity and extensibility in mind.
> It's built upon the existing restart and reboot APIs. The simplicity
> is in new helper functions that are convenient for drivers. The
> extensibility is in the design that doesn't hardcode callback
> arguments, making easy to add new parameters and remove old.
> 
> This is a third attempt to introduce the new API. First was made by
> Guenter Roeck back in 2014, second was made by Thierry Reding in 2017.
> In fact the work didn't stop and recently arm_pm_restart() was removed
> from v5.14 kernel, which was a part of preparatory work started by
> Guenter Roeck. I took into account experience and ideas from the
> previous attempts, extended and polished them.
> 
> Adoption plan
> -------------
> 
> This patchset introduces the new API. It also converts multiple drivers
> and arch code to the new API to demonstrate how it all looks in practice.
> 
> The plan is:
> 
> 1. Merge new API (patches 1-8). This API will co-exist with the old APIs.
> 
> 2. Convert arch code to do_kernel_power_off() (patches 9-21).
> 
> 3. Convert drivers and platform code to the new API.
> 
> 4. Remove obsolete pm_power_off and pm_power_off_prepare variables.
> 
> 5. Make restart-notifier API private to kernel/reboot.c once no users left.
> 
> It's fully implemented here:
> 
> [1] https://github.com/grate-driver/linux/commits/sys-off-handler
> 
> For now I'm sending only the first 25 base patches out of ~180. It's
> preferable to squash 1-2, partially 3 and 4 points of the plan into a
> single patchset to ease and speed up applying of the rest of the patches.
> Majority of drivers and platform patches depend on the base, hence they
> will come later (and per subsystem), once base will land.
> 
> All [1] patches are compile-tested. Tegra and x86 ACPI patches are tested
> on hardware. The remaining should be covered by unit tests (unpublished).
> 
> Results
> -------
> 
> 1. Devices can be powered off properly.
> 
> 2. Global variables are removed from drivers.
> 
> 3. Global pm_power_off and pm_power_off_prepare callback variables are
> removed once all users are converted to the new API. The latter callback
> is removed by patch #25 of this series.
> 
> 4. Ambiguous call chain ordering is prohibited. See patch #5 which adds
> verification of restart handlers priorities, ensuring that they are unique.
> 
> Changelog:
> 
> v3: - Renamed power_handler to sys_off_handler as was suggested by
>       Rafael Wysocki.
> 
>     - Improved doc-comments as was suggested by Rafael Wysocki. Added more
>       doc-comments.
> 
>     - Implemented full set of 180 patches which convert whole kernel in
>       accordance to the plan, see link [1] above. Slightly adjusted API to
>       better suit for the remaining converted drivers.
> 
>       * Added unregister_sys_off_handler() that is handy for a couple old
>         platform drivers.
> 
>       * Dropped devm_register_trivial_restart_handler(), 'simple' variant
>         is enough to have.
> 
>     - Improved "Add atomic/blocking_notifier_has_unique_priority()" patch,
>       as was suggested by Andy Shevchenko. Also replaced down_write() with
>       down_read() and factored out common notifier_has_unique_priority().
> 
>     - Added stop_chain field to struct restart_data and reboot_prep_data
>       after discovering couple drivers wanting that feature.
> 
>     - Added acks that were given to v2.
> 
> v2: - Replaced standalone power-off call chain demo-API with the combined
>       power-off+restart API because this is what drivers want. It's a more
>       comprehensive solution.
> 
>     - Converted multiple drivers and arch code to the new API. Suggested by
>       Andy Shevchenko. I skimmed through the rest of drivers, verifying that
>       new API suits them. The rest of the drivers will be converted once we
>       will settle on the new API, otherwise will be too many patches here.
> 
>     - v2 API doesn't expose notifier to users and require handlers to
>       have unique priority. Suggested by Guenter Roeck.
> 
>     - v2 API has power-off chaining disabled by default and require
>       drivers to explicitly opt-in to the chaining. This preserves old
>       behaviour for existing drivers once they are converted to the new
>       API.
> 
> Dmitry Osipenko (25):
>   notifier: Remove extern annotation from function prototypes
>   notifier: Add blocking_notifier_call_chain_is_empty()
>   notifier: Add atomic/blocking_notifier_has_unique_priority()
>   reboot: Correct typo in a comment
>   reboot: Warn if restart handler has duplicated priority
>   reboot: Warn if unregister_restart_handler() fails
>   reboot: Remove extern annotation from function prototypes
>   kernel: Add combined power-off+restart handler call chain API
>   ARM: Use do_kernel_power_off()
>   csky: Use do_kernel_power_off()
>   riscv: Use do_kernel_power_off()
>   arm64: Use do_kernel_power_off()
>   parisc: Use do_kernel_power_off()
>   xen/x86: Use do_kernel_power_off()
>   sh: Use do_kernel_power_off()
>   x86: Use do_kernel_power_off()
>   ia64: Use do_kernel_power_off()
>   mips: Use do_kernel_power_off()
>   nds32: Use do_kernel_power_off()
>   powerpc: Use do_kernel_power_off()
>   m68k: Switch to new sys-off handler API
>   memory: emif: Use kernel_can_power_off()
>   ACPI: power: Switch to sys-off handler API
>   regulator: pfuze100: Use devm_register_sys_off_handler()
>   reboot: Remove pm_power_off_prepare()
> 
>  arch/arm/kernel/reboot.c               |   4 +-
>  arch/arm64/kernel/process.c            |   3 +-
>  arch/csky/kernel/power.c               |   6 +-
>  arch/ia64/kernel/process.c             |   4 +-
>  arch/m68k/emu/natfeat.c                |   3 +-
>  arch/m68k/include/asm/machdep.h        |   1 -
>  arch/m68k/kernel/process.c             |   5 +-
>  arch/m68k/kernel/setup_mm.c            |   1 -
>  arch/m68k/kernel/setup_no.c            |   1 -
>  arch/m68k/mac/config.c                 |   4 +-
>  arch/mips/kernel/reset.c               |   3 +-
>  arch/nds32/kernel/process.c            |   3 +-
>  arch/parisc/kernel/process.c           |   4 +-
>  arch/powerpc/kernel/setup-common.c     |   4 +-
>  arch/powerpc/xmon/xmon.c               |   3 +-
>  arch/riscv/kernel/reset.c              |  12 +-
>  arch/sh/kernel/reboot.c                |   3 +-
>  arch/x86/kernel/reboot.c               |   4 +-
>  arch/x86/xen/enlighten_pv.c            |   4 +-
>  drivers/acpi/sleep.c                   |  25 +-
>  drivers/memory/emif.c                  |   2 +-
>  drivers/regulator/pfuze100-regulator.c |  38 +-
>  include/linux/notifier.h               |  37 +-
>  include/linux/pm.h                     |   1 -
>  include/linux/reboot.h                 | 305 ++++++++++++--
>  kernel/notifier.c                      |  83 ++++
>  kernel/power/hibernate.c               |   2 +-
>  kernel/reboot.c                        | 556 ++++++++++++++++++++++++-
>  28 files changed, 985 insertions(+), 136 deletions(-)
> 

+CC Linus Walleij, Sebastian Reichel and Philipp Zabel; whom I missed to
include by accident.

https://lore.kernel.org/all/[email-masked]/T/#t