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Commit 787047ee authored by Stephen Boyd's avatar Stephen Boyd Committed by Russell King
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ARM: 8392/3: smp: Only expose /sys/.../cpuX/online if hotpluggable 



Writes to /sys/.../cpuX/online fail if we determine the platform
doesn't support hotplug for that CPU. Furthermore, if the cpu_die
op isn't specified the system hangs when we try to offline a CPU
and it comes right back online unexpectedly. Let's figure this
stuff out before we make the sysfs nodes so that the online file
doesn't even exist if it isn't (at least sometimes) possible to
hotplug the CPU.

Add a new 'cpu_can_disable' op and repoint all 'cpu_disable'
implementations at it because all implementers use the op to
indicate if a CPU can be hotplugged or not in a static fashion.
With PSCI we may need to add a 'cpu_disable' op so that the
secure OS can be migrated off the CPU we're trying to hotplug.
In this case, the 'cpu_can_disable' op will indicate that all
CPUs are hotpluggable by returning true, but the 'cpu_disable' op
will make a PSCI migration call and occasionally fail, denying
the hotplug of a CPU. This shouldn't be any worse than x86 where
we may indicate that all CPUs are hotpluggable but occasionally
we can't offline a CPU due to check_irq_vectors_for_cpu_disable()
failing to find a CPU to move vectors to.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Nicolas Pitre <nico@linaro.org>
Cc: Dave Martin <Dave.Martin@arm.com>
Acked-by: Simon Horman <horms@verge.net.au> [shmobile portion]
Tested-by: default avatarSimon Horman <horms@verge.net.au>
Cc: Magnus Damm <magnus.damm@gmail.com>
Cc: <linux-sh@vger.kernel.org>
Tested-by: default avatarTyler Baker <tyler.baker@linaro.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: default avatarStephen Boyd <sboyd@codeaurora.org>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 57853e89

arch/arm/common/mcpm_platsmp.c

+4 −8
Original line number Diff line number Diff line
@@ -65,14 +65,10 @@ static int mcpm_cpu_kill(unsigned int cpu) 
	return !mcpm_wait_for_cpu_powerdown(pcpu, pcluster);

}



static int mcpm_cpu_disable(unsigned int cpu)

static bool mcpm_cpu_can_disable(unsigned int cpu)

{

	/*

	 * We assume all CPUs may be shut down.

	 * This would be the hook to use for eventual Secure

	 * OS migration requests as described in the PSCI spec.

	 */

	return 0;

	/* We assume all CPUs may be shut down. */

	return true;

}



static void mcpm_cpu_die(unsigned int cpu)
@@ -92,7 +88,7 @@ static struct smp_operations __initdata mcpm_smp_ops = { 
	.smp_secondary_init	= mcpm_secondary_init,

#ifdef CONFIG_HOTPLUG_CPU

	.cpu_kill		= mcpm_cpu_kill,

	.cpu_disable		= mcpm_cpu_disable,

	.cpu_can_disable	= mcpm_cpu_can_disable,

	.cpu_die		= mcpm_cpu_die,

#endif

};

arch/arm/include/asm/smp.h

+1 −0
Original line number Diff line number Diff line
@@ -105,6 +105,7 @@ struct smp_operations { 
#ifdef CONFIG_HOTPLUG_CPU

	int  (*cpu_kill)(unsigned int cpu);

	void (*cpu_die)(unsigned int cpu);

	bool  (*cpu_can_disable)(unsigned int cpu);

	int  (*cpu_disable)(unsigned int cpu);

#endif

#endif

arch/arm/include/asm/smp_plat.h

+9 −0
Original line number Diff line number Diff line
@@ -107,4 +107,13 @@ static inline u32 mpidr_hash_size(void) 
extern int platform_can_secondary_boot(void);

extern int platform_can_cpu_hotplug(void);



#ifdef CONFIG_HOTPLUG_CPU

extern int platform_can_hotplug_cpu(unsigned int cpu);

#else

static inline int platform_can_hotplug_cpu(unsigned int cpu)

{

	return 0;

}

#endif



#endif

arch/arm/kernel/setup.c

+1 −1
Original line number Diff line number Diff line
@@ -1015,7 +1015,7 @@ static int __init topology_init(void) 


	for_each_possible_cpu(cpu) {

		struct cpuinfo_arm *cpuinfo = &per_cpu(cpu_data, cpu);

		cpuinfo->cpu.hotpluggable = 1;

		cpuinfo->cpu.hotpluggable = platform_can_hotplug_cpu(cpu);

		register_cpu(&cpuinfo->cpu, cpu);

	}

arch/arm/kernel/smp.c

+14 −1
Original line number Diff line number Diff line
@@ -175,13 +175,26 @@ static int platform_cpu_disable(unsigned int cpu) 
	if (smp_ops.cpu_disable)

		return smp_ops.cpu_disable(cpu);



	return 0;

}



int platform_can_hotplug_cpu(unsigned int cpu)

{

	/* cpu_die must be specified to support hotplug */

	if (!smp_ops.cpu_die)

		return 0;



	if (smp_ops.cpu_can_disable)

		return smp_ops.cpu_can_disable(cpu);



	/*

	 * By default, allow disabling all CPUs except the first one,

	 * since this is special on a lot of platforms, e.g. because

	 * of clock tick interrupts.

	 */

	return cpu == 0 ? -EPERM : 0;

	return cpu != 0;

}



/*

 * __cpu_disable runs on the processor to be shutdown.

 */