On Fri, Jun 07, 2013 at 05:44:33PM +0100, Stephen Warren wrote: > On 06/07/2013 03:36 AM, Joseph Lo wrote: > > The normal CPU hotplug flow in kernel and the flow for Tegra we expected, > > is checking the CPU ID is OK for hotplug by "tegra_cpu_disable", the CPU > > that would be hotplugged runs into a power-gate state by "tegra_cpu_die", > > then the other CPU waits for the CPU that was hotplugged in reset and > > clock gate it by "tegra_cpu_kill". That means we don't support the CPU > > being stopped or put into offline by trigger "tegra_cpu_kill" directly. > > It may cause a busy loop for waiting CPU in reset. > > > > After the commit "62e930e reboot: rigrate shutdown/reboot to boot cpu", > > we remove "disable_nonboot_cpus" when kernel_{restart,halt,power_off}. > > But the ARM kernel trigger "send_smp_stop" when machine_shutdown, that > > would cause the "tegra_cpu_kill" directly without "tegra_cpu_die" first. > > > > We hook "disable_nonboot_cpus" in "reboot_notifier" to avoid that happens. > > And it can work for reboot, shutdown, halt and kexec. > > I don't believe this is the correct solution. > > If the semantics of cpu_kill/cpu_die are such that it's legal to call > only cpu_kill without having cause cpu_die to run on the killed CPU > first, then Tegra's implementation is buggy. We should simply fix that, > rather than avoiding this by forcing a different order for the calls to > cpu_kill/cpu_die. > > If the semantics of cpu_kill/cpu_die are such that one /must/ cause > cpu_die to run on the killed CPU before cpu_kill can be used on it, then > there's a bug in the code that isn't doing that. > > I'm CCing a few people in an attempt to find out exactly what the > expected semantics are for cpu_kill/cpu_die; is it legal to call > cpu_kill without having first caused cpu_die to execute? By cpu_kill, do you mean platform_cpu_kill called from __cpu_die? If so, __cpu_die and cpu_die are definitely supposed to be treated as a pair, since they synchronise via the cpu_died completion. Will -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html