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. Several other restart drivers for arm, all directly calling arm_pm_restart, are in the process of being integrated into the kernel. All those drivers would benefit from the new API. 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 notifier to solve the described problems. 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. By using the priority field in the notifier block, callers can control notifier execution sequence and thus ensure that the notifier with the optimal restart capabilities for a given system is called first. Since the first revision of this patchset, a number of separate patch submissions have been made which either depend on it or could make use of it. http://www.spinics.net/linux/lists/arm-kernel/msg344796.html registers three notifiers. https://lkml.org/lkml/2014/7/8/962 would benefit from it. 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 modifies the restart-poweroff driver to no longer call arm_pm_restart directly but machine_restart. This is done to avoid calling arm_pm_restart from more than one place. The change makes the driver architecture independent, so it would be possible to drop the arm dependency from its Kconfig entry. Patch 5 and 6 convert existing restart handlers in the watchdog subsystem to use the restart notifier. Patch 7 unexports arm_pm_restart to ensure that no one gets the idea to implement a restart handler as module. --- v4: Document restart notifier priorities Select 128 as default priority for newly introduced notifiers Fix checkpatch warning (line too long) in moxart patch v3: Drop RFC. Add kernel_restart_notify wrapper function to execute notifier Improve documentation. Move restart_notifier_list into kernel/reboot.c and make it static. v2: Add patch 4. Only call blocking notifier call chain if arm_pm_restart was not set. -- 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
