• Guenter Roeck's avatar
    kernel: add support for kernel restart handler call chain · b63adb97
    Guenter Roeck authored
    Various drivers implement architecture and/or device specific means to
    restart (reset) the system.  Various mechanisms have been implemented to
    support those schemes.  The best known mechanism is arm_pm_restart, which
    is a function pointer to be set either from platform specific code or from
    drivers.  Another mechanism is to use hardware watchdogs to issue a reset;
    this mechanism is used if there is no other method available to reset a
    board or system.  Two examples are alim7101_wdt, which currently uses the
    reboot notifier to trigger a reset, and moxart_wdt, which registers the
    arm_pm_restart function.
    The existing mechanisms have a number of drawbacks.  Typically only one
    scheme to restart the system is supported (at least if arm_pm_restart is
    used).  At least in theory there can be multiple means to restart the
    system, some of which may be less desirable (for example one mechanism may
    only reset the CPU, while another may reset the entire system).  Using
    arm_pm_restart can also be racy if the function pointer is set from a
    driver, as the driver may be in the process of being unloaded when
    arm_pm_restart is called.  Using the reboot notifier is always racy, as it
    is unknown if and when other functions using the reboot notifier have
    completed execution by the time the watchdog fires.
    Introduce a system restart handler call chain to solve the described
    problems.  This call chain is expected to be executed from the
    architecture specific machine_restart() function.  Drivers providing
    system restart functionality (such as the watchdog drivers mentioned
    above) are expected to register with this call chain.  By using the
    priority field in the notifier block, callers can control restart handler
    execution sequence and thus ensure that the restart handler with the
    optimal restart capabilities for a given system is called first.
    Signed-off-by: default avatarGuenter Roeck <linux@roeck-us.net>
    Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
    Acked-by: default avatarHeiko Stuebner <heiko@sntech.de>
    Cc: Russell King <linux@arm.linux.org.uk>
    Cc: Wim Van Sebroeck <wim@iguana.be>
    Cc: Maxime Ripard <maxime.ripard@free-electrons.com>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Jonas Jensen <jonas.jensen@gmail.com>
    Cc: Randy Dunlap <rdunlap@infradead.org>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
    Cc: David Woodhouse <dwmw2@infradead.org>
    Cc: Tomasz Figa <t.figa@samsung.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
reboot.c 12.5 KB