Guenter, On Tue, Aug 19, 2014 at 5:45 PM, Guenter Roeck <linux@xxxxxxxxxxxx> wrote: > 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: Guenter Roeck <linux@xxxxxxxxxxxx> > Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx> > Acked-by: Heiko Stuebner <heiko@xxxxxxxxx> > --- > v7: Rebased to v3.17-rc1 > v6: Use atomic notifier call chain > v5: Function renames: > register_restart_notifier -> register_restart_handler > unregister_restart_notifier -> unregister_restart_handler > kernel_restart_notify -> do_kernel_restart > v4: Document and suggest values for notifier priorities > v3: Add kernel_restart_notify wrapper function to execute notifier. > Improve documentation. > Move restart_notifier_list into kernel/reboot.c and make it static. > v2: No change. > > include/linux/reboot.h | 3 ++ > kernel/reboot.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 84 insertions(+) Reviewed-by: Doug Anderson <dianders@xxxxxxxxxxxx> Tested-by: Doug Anderson <dianders@xxxxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
