On 12/21/2012 02:58 AM, Joseph Lo wrote: > On Fri, 2012-12-21 at 01:01 +0800, Stephen Warren wrote: >> On 12/19/2012 07:28 PM, Joseph Lo wrote: >>> The tegra_cpu_die was be executed by the CPU itslf. So the clock gating >>> procedure won't be executed after the CPU hardware shutdown code. Moving >>> the clock gating procedure to tegra_cpu_kill that will be run by another >>> CPU after the CPU died. >> >> Hmmm. I wonder if this is enough to make kexec-on-Tegra-with-SMP-enabled >> work without explicitly hot-unplugging all the CPUs first... An >> implementation of cpu_kill() was a major part of what was missing. I >> thought an implementation of cpu_kill() would require a bunch of code >> from cpu_die() too. Does this patch assume cpu_die() has executed first, >> and only then cpu_kill() will work, or can cpu_kill() be used on its own? >> > Yes, the tegra_cpu_die must be run first then tegra_cpu_kill. Because > the tegra_cpu_die shutdown the CPU by itself, then we can clock gate the > CPU in tegra_cpu_kill. If the tegra_cpu_kill be run itself, the system > will be hung in wait_for_reset(CPU). > > About the kexec issue, it's complicate. Your solution should be the > right solution. And we should implement the hardware shutdown code in > cpu_die not cpu_kill. I suspect this issue can be reproduced on all ARM > platform. Because the smp_send_stop can't really shutdown the secondary > CPU core if just call machine_shutdown without disable_nonboot_cpu. And > in platform_shutdown and platform_reboot case, the secondary CPU already > been offlined and killed before this function be called. Does any other > ARM SMP platform can run kexec without any issue? > > (I will check if we can do some HW shutdown in tegra_cpu_kill. For ex, > just clock gate the CPU without wait_for_reset.) Will, Joseph's thoughts above pretty much match mine re: kexec. In the kexec thread I started earlier, I talked about replacing: void machine_shutdown(void) { #ifdef CONFIG_SMP smp_send_stop(); #endif } with something like: void machine_shutdown(void) { #ifdef CONFIG_HOTPLUG_CPU disable_nonboot_cpus(); #elifdef CONFIG_SMP smp_send_stop(); #endif } and you'd responded "I think you're better off using what we currently have and hanging your code off platform_cpu_kill.". What exactly did you mean by "what we currently have"; did you mean that cpu_kill() should work without cpu_die() having executed on the target CPU itself first, so Tegra should simply implement cpu_kill()? As Joseph says above, I'm not sure that will work. Any more detailed thoughts you have here would be greatly appreciated. Thanks. -- 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