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. Patch 1 of this series implements the notifier function. Patches 2 and 3 implement calling the notifier chain from arm and arm64 restart code. Patch 4 and 5 convert existing restart handlers in the watchdog subsystem to use the restart notifier. Patch 6 unexports arm_pm_restart to ensure that no one gets the idea to implement a restart handler as module. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
