Skip to contentSkip to conversation

ARM: rockchip: Add cpu hotplug support for RK3XXX SoCs

PATCH New Romain Perier 2 participants 5 messages Jul 17, 2014 – Jul 18, 2014

Subsystems (3)
Arm (32-bit) Arm sub-architectures Arm Rockchip
lore
Share & tools
lore

Romain Perier

author
#0 lore raw

PATCH 1/1 ARM: rockchip: Add cpu hotplug support for RK3XXX SoCs

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 <[email protected]>
---
 arch/arm/mach-rockchip/platsmp.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)
arch/arm/mach-rockchip/platsmp.c +31 -0
index 910835d..7c1299a 100644
@@ -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);
Signature · 1 line
1.9.1
#1 lore raw

PATCH 1/1 ARM: rockchip: Add cpu hotplug support for RK3XXX SoCs

arch/arm/mach-rockchip/platsmp.c static void __init rockchip_smp_prepare_cpus(unsigned int max_cpus) · line 190

Quoted 8 lines · Romain Perier
arch/arm/mach-rockchip/platsmp.c +8 -0
+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.

Signature · 2 lines
FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up
according to speedtest.net.
author
#2 lore raw

PATCH 1/1 ARM: rockchip: Add cpu hotplug support for RK3XXX SoCs

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.

Quoted 14 lines · Russell King - ARM Linux

arch/arm/mach-rockchip/platsmp.c static void __init rockchip_smp_prepare_cpus(unsigned int max_cpus) · line 190

Quoted 8 lines · Romain Perier
arch/arm/mach-rockchip/platsmp.c +8 -0
+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.

#3 lore raw

PATCH 1/1 ARM: rockchip: Add cpu hotplug support for RK3XXX SoCs

Quoted 6 lines · Romain Perier

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()?

Signature · 2 lines
FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up
according to speedtest.net.
author
#4 lore raw

PATCH 1/1 ARM: rockchip: Add cpu hotplug support for RK3XXX SoCs

Le 18/07/2014 10:29, Russell King - ARM Linux a ?crit :

Quoted 39 lines · Romain Perier
Quoted 6 lines

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();
Quoted 3 lines

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