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    SubjectRe: [PATCH v3 00/47] kernel: Add support for power-off handler call chain
    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@lxorguk.ukuu.org.uk>
    > Cc: Alexander Graf <agraf@suse.de>
    > Cc: Andrew Morton <akpm@linux-foundation.org>
    > Cc: Geert Uytterhoeven <geert@linux-m68k.org>
    > cc: Heiko Stuebner <heiko@sntech.de>
    > Cc: Lee Jones <lee.jones@linaro.org>
    > Cc: Len Brown <len.brown@intel.com>
    > Cc: Pavel Machek <pavel@ucw.cz>
    > Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
    > Cc: Romain Perier <romain.perier@gmail.com>
    > --
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    --
    balbi
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