On Wed, Oct 29, 2014 at 02:22:44PM +0100, Johan Hovold wrote: > On Wed, Oct 29, 2014 at 01:10:20PM +0000, Russell King - ARM Linux wrote: > > On Wed, Oct 29, 2014 at 01:34:18PM +0100, Johan Hovold wrote: > > > On Tue, Oct 28, 2014 at 03:16:10PM +0000, Russell King - ARM Linux wrote: > > > > And how is that different from having a set of power-off handlers, and > > > > reporting when each individual one fails? Don't you want to know if > > > > your primary high priority reboot handler fails, just as much as you > > > > want to know if your final last-resort power-off handler fails? > > > > > > Good point. Failed power-off should probably be logged by the power-off > > > call chain implementation (which seems to makes notifier chains a bad > > > fit). > > > > > > And what about any power-off latencies? Should this always be dealt with > > > in the power-off handler? > > > > > > Again, if it's predictable and high, as in the OMAP RTC case, it should > > > go in the handler. But what if it's just normal bus latencies > > > (peripheral busses, i2c, or whatever people may come up with)? > > > > > > Should there always be a short delay before calling the next handler? > > > > If the handler has determined that it has failed, then why delay before > > trying the next handler? At the point it has decided it has failed, > > surely that's after it has waited sufficient time to determine that > > failure? > > The current handlers we have are not expecting any other handler to be > run after they return. My question was whether all these handlers should > get a short mdelay added to them (e.g. to compensate for bus latencies) Some of them do add a delay. > or if this could be done in the power-off handler (e.g. before printing > the error message). > That might make sense, but it would have to be configurable, since the delay is platform specific and power-off handler does not know how long to wait (the longest delay I have seen is 10 seconds). > > > > Or different from having no power-off handlers. > > > > > > That is actually quite different, as in that case we call machine_halt > > > instead (via kernel_halt). > > > > Today, ARM does exactly what x86 does. If there's no power off handler > > registered, machine_power_off() shuts down other CPUs and returns. > > No, if there are no power-off handlers registered, kernel/reboot.c will > never call machine_power_off: > > /* Instead of trying to make the power_off code look like > * halt when pm_power_off is not set do it the easy way. > */ > if ((cmd == LINUX_REBOOT_CMD_POWER_OFF) && !pm_power_off) > cmd = LINUX_REBOOT_CMD_HALT; > > So in that case on arm, a system-halted message is printed, and we never > return to user-space. > Some architectures do that, or go into an endless loop. Others do return from machine_power_off. Having a well defined behavior would be nice (such as dumping an error mesasge and calling machine_halt if machine_power_off returns). Only question would be where to put it. kernel_power_off() might be a good place; only problem is that there are direct callers of machine_power_off(). Guenter -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
