On Mon, Jun 30, 2014 at 08:59:47PM +0100, Russell King - ARM Linux wrote: > On Mon, Jun 30, 2014 at 12:11:33PM -0700, Guenter Roeck 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. > > > > 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. > > I think you need to restructure stuff somewhat, because I think > you've missed drivers/power/reset/ entirely, or at least you've > missed drivers/power/reset/restart-poweroff.c which calls > arm_pm_restart directly. I'm not quite sure how we ended up with > that... > Yes, guess I missed (and did not really expect) that arm_pm_restart is called from multiple places. What is restart-poweroff supposed to do in the first place, and why doesn't it call machine_restart() ? If it is what I think it is, ie a fallback for pm_power_off, it could be made generic and does not really have to depend on ARM. Thanks, Guenter -- 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
