[PATCH] ARM: reboot: disable nonboot CPUs

[PATCH] ARM: reboot: disable nonboot CPUs

[Per Forlin]

Disable the nonboot CPUs to safely migrate tasks and interrupts
to the boot CPU. This will prevent the nonboot CPUs to
interfer or block the boot CPU from being able to reboot
the system successfully.

This reboot issue was detected on u8500 when using ab8500 to initaite a
system restart. The issue happens because smp_send_stop() stops the CPUs
wihouth migrating all resources.
If not issuing smp_send_stop() u8500 reboots successfully.

It's optional to support CONFIG_PM_SLEEP_SMP therefore smp_send_stop()
can't simply be replaced by disable_nonboot_cpus()

Signed-off-by: Per Forlin <per.forlin@stericsson.com>
---
 arch/arm/kernel/process.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 864580a..aab4f81 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -239,6 +239,7 @@ __setup("reboot=", reboot_setup);
 
 void machine_shutdown(void)
 {
+	disable_nonboot_cpus();
 #ifdef CONFIG_SMP
 	smp_send_stop();
 #endif
-- 
1.7.10

[PATCH] ARM: reboot: disable nonboot CPUs

[Russell King - ARM Linux]

On Wed, Jul 04, 2012 at 09:51:02AM +0200, Per Forlin wrote:
> Disable the nonboot CPUs to safely migrate tasks and interrupts
> to the boot CPU. This will prevent the nonboot CPUs to
> interfer or block the boot CPU from being able to reboot
> the system successfully.
> 
> This reboot issue was detected on u8500 when using ab8500 to initaite a
> system restart. The issue happens because smp_send_stop() stops the CPUs
> wihouth migrating all resources.
> If not issuing smp_send_stop() u8500 reboots successfully.
> 
> It's optional to support CONFIG_PM_SLEEP_SMP therefore smp_send_stop()
> can't simply be replaced by disable_nonboot_cpus()

I don't understand what or why you're trying to do this, it seems to be
unreliable to rely upon conditional sleep support to make system reboot
to work.

Yes, we know at the moment that smp_send_stop() results in the secondary
CPUs ending up spinning in the kernel, which is then potentially replaced
buy whatever happens after boot, but short of creating a new per-subarch
function, I don't see much other alternative.

Doesn't your kernel restart trigger a system hardware reset in any case?
That's about the only reliable way to do a system restart with SMP.

[PATCH] ARM: reboot: disable nonboot CPUs

[Per Förlin]

On 07/04/2012 11:50 AM, Russell King - ARM Linux wrote:
> On Wed, Jul 04, 2012 at 09:51:02AM +0200, Per Forlin wrote:
>> Disable the nonboot CPUs to safely migrate tasks and interrupts
>> to the boot CPU. This will prevent the nonboot CPUs to
>> interfer or block the boot CPU from being able to reboot
>> the system successfully.
>>
>> This reboot issue was detected on u8500 when using ab8500 to initaite a
>> system restart. The issue happens because smp_send_stop() stops the CPUs
>> wihouth migrating all resources.
>> If not issuing smp_send_stop() u8500 reboots successfully.
>>
>> It's optional to support CONFIG_PM_SLEEP_SMP therefore smp_send_stop()
>> can't simply be replaced by disable_nonboot_cpus()
> 
> I don't understand what or why you're trying to do this, it seems to be
> unreliable to rely upon conditional sleep support to make system reboot
> to work.
> 
> Yes, we know at the moment that smp_send_stop() results in the secondary
> CPUs ending up spinning in the kernel, which is then potentially replaced
> buy whatever happens after boot, but short of creating a new per-subarch
> function, I don't see much other alternative.
> 
> Doesn't your kernel restart trigger a system hardware reset in any case?
> That's about the only reliable way to do a system restart with SMP.

Thanks for your reply,

The system doesn't reset in the case when calling smp_send_stop().
This is because the reboot mechanism has a couple of dependencies and some of them lives on CPU1.
The reboot is performed by an external chip that eventually switches of a regulator that triggers the restart.
After smp_send_stop() the mailbox communication with the external chip fails, therefore the reboot doesn't happen.
Right now I don't know in detail why this communication fails.

Here are my options
1. Run disble_nonboot_cpus() to migrate resources from CPU1 to CPU0
2. Skip calling smp_send_stop(), that works fine on my platform.
3. Make sure there are no reboot-dependencies on CPU1. Currently I lack the detail understanding of what these dependencies are.

BR
Per