On Fri, Dec 21, 2012 at 09:23:17PM +0000, Stephen Warren wrote:

On 12/21/2012 02:58 AM, Joseph Lo wrote:

quoted

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.".

Sorry for being vague: I just meant that the code as it stands in mainline
is better than calling disable_nonboot_cpus(), because the latter seems to
require all the secondary cores to hit the idle loop, notice that they are
not online, and then call cpu_die. We really need this sequence to be
synchronous wrt the CPU initiating the kexec.

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.

I guess this comes down to the different between cpu_die/cpu_kill and
whether you actually need cpu_die if you're not planning on returning to
the same kernel that you left. If you really need to call cpu_die, then we
need to figure out a way to do that whilst ensuring that only one CPU is
left standing at the time we start copying the new kernel into place.

Will