On Sun, 6 Jul 2014 16:38:14 -0700 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 mutliple 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. > > To solve the problem, introduce a system restart notifier. This notifier > is expected to be called 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 notifier. It all looks sane to my unfamiliar eye. > /* > + * Notifier list for kernel code which wants to be called > + * to restart the system. > + */ hm, is this all we have to say? > --- a/kernel/reboot.c > +++ b/kernel/reboot.c > @@ -104,6 +104,38 @@ int unregister_reboot_notifier(struct notifier_block *nb) > } > EXPORT_SYMBOL(unregister_reboot_notifier); > > +/** > + * register_restart_notifier - Register function to be called to reset > + * the system > + * @nb: Info about notifier function to be called > + * > + * Registers a function with the list of functions > + * to be called to restart the system. > + * > + * Currently always returns zero, as blocking_notifier_chain_register() > + * always returns zero. > + */ This would be a good place to describe what those notifier callbacks actually do. Why they exist, what their role is, under what circumstances they are called, what values they should return, etc. -- 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
