[PATCH] ARM: rockchip: Add cpu hotplug support for RK3XXX SoCs

[PATCH] ARM: rockchip: Add cpu hotplug support for RK3XXX SoCs

[Romain Perier]

Adds ability to shutdown all CPUs except the first one
(since it might be special for a lot of platforms).
It is now possible to use kexec which requires such a feature.

Signed-off-by: Romain Perier <romain.perier@gmail.com>
---
 arch/arm/mach-rockchip/platsmp.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/arch/arm/mach-rockchip/platsmp.c b/arch/arm/mach-rockchip/platsmp.c
index 910835d..7c1299a 100644
--- a/arch/arm/mach-rockchip/platsmp.c
+++ b/arch/arm/mach-rockchip/platsmp.c
@@ -21,6 +21,7 @@
 #include <linux/of_address.h>
 
 #include <asm/cacheflush.h>
+#include <asm/cp15.h>
 #include <asm/smp_scu.h>
 #include <asm/smp_plat.h>
 #include <asm/mach/map.h>
@@ -178,8 +179,38 @@ static void __init rockchip_smp_prepare_cpus(unsigned int max_cpus)
 		pmu_set_power_domain(0 + i, false);
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+static DECLARE_COMPLETION(cpu_died);
+
+static int rockchip_cpu_kill(unsigned int cpu)
+{
+	if (!wait_for_completion_timeout(&cpu_died, msecs_to_jiffies(1000))) {
+		pr_err("CPU%d: didn't die correctly\n", cpu);
+		return 0;
+	}
+	pmu_set_power_domain(0 + cpu, false);
+	return 1;
+}
+
+
+static void rockchip_cpu_die(unsigned int cpu)
+{
+	complete(&cpu_died);
+	flush_cache_louis();
+
+	v7_exit_coherency_flush(louis);
+
+	while(1)
+		cpu_do_idle();
+}
+#endif
+
 static struct smp_operations rockchip_smp_ops __initdata = {
 	.smp_prepare_cpus	= rockchip_smp_prepare_cpus,
 	.smp_boot_secondary	= rockchip_boot_secondary,
+#ifdef CONFIG_HOTPLUG_CPU
+	.cpu_kill		= rockchip_cpu_kill,
+	.cpu_die		= rockchip_cpu_die,
+#endif
 };
 CPU_METHOD_OF_DECLARE(rk3066_smp, "rockchip,rk3066-smp", &rockchip_smp_ops);
-- 
1.9.1

[PATCH] ARM: rockchip: Add cpu hotplug support for RK3XXX SoCs

[Russell King - ARM Linux]

On Thu, Jul 17, 2014 at 05:11:50PM +0000, Romain Perier wrote:
> +static DECLARE_COMPLETION(cpu_died);
> +
> +static int rockchip_cpu_kill(unsigned int cpu)
> +{
> +	if (!wait_for_completion_timeout(&cpu_died, msecs_to_jiffies(1000))) {
> +		pr_err("CPU%d: didn't die correctly\n", cpu);
> +		return 0;
> +	}

Please explain the point of this cpu_died thing.

I think you should read arch/arm/kernel/smp.c, searching for cpu_died
in there.

-- 
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according to speedtest.net.

[PATCH] ARM: rockchip: Add cpu hotplug support for RK3XXX SoCs

[Romain Perier]

Hi all,

you're probably talking about __cpu_die at 
http://lxr.free-electrons.com/source/arch/arm/kernel/smp.c#L223 . The 
problem being that the thread below which executes cpu_die completes the 
completion before executing smp_ops.cpu_die. So smp_ops.cpu_kill might 
be executed before smp_ops.cpu_die (in some cases cache coherency would 
not be turned off). Note that almost all SoCs do the same thing.


On 18/07/2014 00:14, Russell King - ARM Linux wrote:
> On Thu, Jul 17, 2014 at 05:11:50PM +0000, Romain Perier wrote:
>> +static DECLARE_COMPLETION(cpu_died);
>> +
>> +static int rockchip_cpu_kill(unsigned int cpu)
>> +{
>> +	if (!wait_for_completion_timeout(&cpu_died, msecs_to_jiffies(1000))) {
>> +		pr_err("CPU%d: didn't die correctly\n", cpu);
>> +		return 0;
>> +	}
> Please explain the point of this cpu_died thing.
>
> I think you should read arch/arm/kernel/smp.c, searching for cpu_died
> in there.
>

[PATCH] ARM: rockchip: Add cpu hotplug support for RK3XXX SoCs

[Russell King - ARM Linux]

On Fri, Jul 18, 2014 at 08:16:02AM +0200, Romain Perier wrote:
> you're probably talking about __cpu_die at  
> http://lxr.free-electrons.com/source/arch/arm/kernel/smp.c#L223 . The  
> problem being that the thread below which executes cpu_die completes the  
> completion before executing smp_ops.cpu_die. So smp_ops.cpu_kill might  
> be executed before smp_ops.cpu_die (in some cases cache coherency would  
> not be turned off). Note that almost all SoCs do the same thing.

Look at what's happening:

	CPU0				CPU1
	wait_for_completion_timeout()
					idle_task_exit()
					flush_cache_louis()
					complete(&cpu_died);

At this point, it is safe for CPU1 to be powered down.

	smp_ops.cpu_kill(cpu);
					flush_cache_louis();
					smp_ops.cpu_die(cpu);

If we include your code at that point, then the sequence in totality
becomes:

	wait_for_completion_timeout()
					idle_task_exit()
					flush_cache_louis()
					complete(&cpu_died);
	--- rockchip_cpu_kill ---
	wait_for_completion_timeout()
					flush_cache_louis();
					--- rockchip_cpu_die ---
					complete(&cpu_died);
	pmu_set_power_domain(0 + cpu, false);
					flush_cache_louis();
					v7_exit_coherency_flush(louis);
					while(1)
						cpu_do_idle();

So, I repeat my question.  What is the point of your additional wait
in rockchip_cpu_kill() and complete in rockchip_cpu_die()?

-- 
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according to speedtest.net.

[PATCH v1] ARM: rockchip: Add cpu hotplug support for RK3XXX SoCs

[Romain Perier]

Le 18/07/2014 10:29, Russell King - ARM Linux a ?crit :
> On Fri, Jul 18, 2014 at 08:16:02AM +0200, Romain Perier wrote:
>> you're probably talking about __cpu_die at
>> http://lxr.free-electrons.com/source/arch/arm/kernel/smp.c#L223 . The
>> problem being that the thread below which executes cpu_die completes the
>> completion before executing smp_ops.cpu_die. So smp_ops.cpu_kill might
>> be executed before smp_ops.cpu_die (in some cases cache coherency would
>> not be turned off). Note that almost all SoCs do the same thing.
> Look at what's happening:
>
> 	CPU0				CPU1
> 	wait_for_completion_timeout()
> 					idle_task_exit()
> 					flush_cache_louis()
> 					complete(&cpu_died);
>
> At this point, it is safe for CPU1 to be powered down.
>
> 	smp_ops.cpu_kill(cpu);
> 					flush_cache_louis();
> 					smp_ops.cpu_die(cpu);
>
> If we include your code at that point, then the sequence in totality
> becomes:
>
> 	wait_for_completion_timeout()
> 					idle_task_exit()
> 					flush_cache_louis()
> 					complete(&cpu_died);
> 	--- rockchip_cpu_kill ---
> 	wait_for_completion_timeout()
> 					flush_cache_louis();
> 					--- rockchip_cpu_die ---
> 					complete(&cpu_died);
> 	pmu_set_power_domain(0 + cpu, false);
> 					flush_cache_louis();
> 					v7_exit_coherency_flush(louis);
> 					while(1)
> 						cpu_do_idle();
>
> So, I repeat my question.  What is the point of your additional wait
> in rockchip_cpu_kill() and complete in rockchip_cpu_die()?
>
Mhhh... you're right... my bad ! So either smp_ops.cpu_kill(cpu) is 
executed before smp_ops.cpu_die and in this case it is safe to power 
down the cpu. or smp_ops.cpu_die(cpu) is executed before 
smp_ops.cpu_kill(due) and it is safe too.

I will send a new patch (v2)

Romain