Re: [PATCH v3 00/47] kernel: Add support for power-off handler call chain

[Felipe Balbi]

Adding Johan, who's working on RTC power off for AM335x devices

On Mon, Oct 27, 2014 at 08:55:07AM -0700, Guenter Roeck wrote:
> Various drivers implement architecture and/or device specific means to
> remove power from the system.  For the most part, those drivers set the
> global variable pm_power_off to point to a function within the driver.
> 
> This mechanism has a number of drawbacks.  Typically only one means
> to remove power is supported (at least if pm_power_off is used).
> At least in theory there can be multiple means to remove power, some of
> which may be less desirable.  For example, one mechanism might power off the
> entire system through an I/O port or gpio pin, while another might power off
> a board by disabling its power controller. Other mechanisms may really just
> execute a restart sequence or drop into the ROM monitor, or put the CPU into
> sleep mode.  Using pm_power_off can also be racy if the function pointer is
> set from a driver built as module, as the driver may be in the process of
> being unloaded when pm_power_off is called.  If there are multiple power-off
> handlers in the system, removing a module with such a handler may
> inadvertently reset the pointer to pm_power_off to NULL, leaving the system
> with no means to remove power.
> 
> Introduce a system power-off handler call chain to solve the described
> problems.  This call chain is expected to be executed from the architecture
> specific machine_power_off() function.  Drivers providing system power-off
> functionality are expected to register with this call chain.  By using the
> priority field in the notifier block, callers can control power-off handler
> execution sequence and thus ensure that the power-off handler with the
> optimal capabilities to remove power for a given system is called first.
> A call chain instead of a single call to the highest priority handler is
> used to provide fallback: If multiple power-off handlers are installed,
> all handlers will be called until one actually succeeds to power off the
> system.
> 
> Patch 01/47 implements the power-off handler API.
> 
> Patches 02/47 to 04/47 are cleanup patches to prepare for the move of
> pm_power_off to a common location.
> 
> Patches 05/47 to 07/47 remove references to pm_power_off from devicetree
> bindings descriptions.
> 
> Patch 08/47 moves the pm_power_off variable from architecture code to
> kernel/reboot.c. 
> 
> Patches 09/47 to 34/47 convert various drivers to register with the kernel
> power-off handler instead of setting pm_power_off directly.
> 
> Patches 35/47 to 46/47 do the same for architecture code.
> 
> Patch 47/47 finally removes pm_power_off.
> 
> For the most part, the individual patches include explanations why specific
> priorities were chosen, at least if the selected priority is not the default
> priority. Subsystem and architecture maintainers are encouraged to have a look
> at the selected priorities and suggest improvements.
> 
> I ran the final code through my normal build and qemu tests. Results are
> available at http://server.roeck-us.net:8010/builders in the 'poweroff-handler'
> column. I also built all available configurations for arm, mips, powerpc,
> m68k, and sh architectures.
> 
> The series is available in branch poweroff-handler of my repository at
> git://git.kernel.org/pub/scm/linux/kernel/git/groeck/linux-staging.git.
> It is based on 3.18-rc2.
> 
> A note on Cc: In the initial submission I had way too many Cc:, causing the
> patchset to be treated as spam by many mailers and mailing list handlers,
> which of course defeated the purpose. This time around I am cutting down
> the distribution list down significantly. My apologies to anyone I may have
> failed to copy this time around.
> 
> Important changes since v2:
> - Rebased series to v3.18-rc2.
> - Do not hold any locks while executing the power-off call chain.
>   This ensures that power-off handlers are executed in the state
>   selected by the machine_power_off function for a given architecture,
>   ie without changing the current semantics of power-off callbacks and
>   machine_power_off functions.
>   Power-off handler registration and de-registration is handled in atomic
>   context with interrupts disabled to ensure that those functions are not
>   interrupted by code which powers off the system.
> - Use [xxx_]power_off[_xxx] instead of [xxx_]poweroff[_xxx] for newly
>   introduced function and variable names.
> - Use power-off instead of poweroff in descriptive text and comments.
> - Replace POWEROFF_PRIORITY_xxx with POWER_OFF_PRIORITY_xxx
> - Use ACPI: instead of acpi: for messages in acpi code.
> 
> Important changes since v1:
> - Rebased series to v3.18-rc1.
> - Use raw notifier with spinlock protection instead of atomic notifiers,
>   since some power-off handlers need to have interrupts enabled.
> - Renamed API functions from _poweroff to _power_off.
> - Added various Acks.
> - Build tested all configurations for arm, powerpc, and mips architectures.
> - Fixed two compile errors in mips patch.
> - Replaced dev_err and pr_err with dev_warn and pr_warn if an error is not
>   fatal.
> - Provide managed resources API and use where appropriate.
> - Provide and use definitions for standard priorities.
> - Added patches to convert newly introduced power-off handlers.
> - Various minor changes.
> 
> Important changes since RFC:
> - Move API to new file kernel/power/power_off_handler.c.
> - Move pm_power_off pointer to kernel/power/power_off_handler.c. Call
>   pm_power_off from do_kernel_power_off, and only call do_kernel_power_off
>   from architecture code instead of calling both pm_power_off and
>   do_kernel_power_off.
> - Provide additional API function register_power_off_handler_simple
>   to simplify conversion of architecture code.
> - Provide additional API function have_kernel_power_off to check if
>   a power-off handler was installed.
> - Convert all drivers and architecture code to use the new API.
> - Remove pm_power_off as last patch of the series.
> 
> Cc: Alan Cox <gnomes@xxxxxxxxxxxxxxxxxxx>
> Cc: Alexander Graf <agraf@xxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> cc: Heiko Stuebner <heiko@xxxxxxxxx>
> Cc: Lee Jones <lee.jones@xxxxxxxxxx>
> Cc: Len Brown <len.brown@xxxxxxxxx>
> Cc: Pavel Machek <pavel@xxxxxx>
> Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
> Cc: Romain Perier <romain.perier@xxxxxxxxx>
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-- 
balbi

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