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: Simon Horman <horms@verge.net.au>
Cc: Magnus Damm <magnus.damm@gmail.com>
Cc: <linux-sh@vger.kernel.org>
Tested-by: Tyler Baker <tyler.baker@linaro.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

5 files changed, 6 insertions, 6 deletions

diff --git a/arch/arm/mach-shmobile/common.h b/arch/arm/mach-shmobile/common.h
index 476092b..8d27ec5 100644
--- a/arch/arm/mach-shmobile/common.h
+++ b/arch/arm/mach-shmobile/common.h
@@ -13,7 +13,7 @@ extern void shmobile_smp_boot(void);
 extern void shmobile_smp_sleep(void);
 extern void shmobile_smp_hook(unsigned int cpu, unsigned long fn,
 			      unsigned long arg);
-extern int shmobile_smp_cpu_disable(unsigned int cpu);
+extern bool shmobile_smp_cpu_can_disable(unsigned int cpu);
 extern void shmobile_boot_scu(void);
 extern void shmobile_smp_scu_prepare_cpus(unsigned int max_cpus);
 extern void shmobile_smp_scu_cpu_die(unsigned int cpu);
diff --git a/arch/arm/mach-shmobile/platsmp.c b/arch/arm/mach-shmobile/platsmp.c
index 3923e09..b23378f 100644
--- a/arch/arm/mach-shmobile/platsmp.c
+++ b/arch/arm/mach-shmobile/platsmp.c
@@ -31,8 +31,8 @@ void shmobile_smp_hook(unsigned int cpu, unsigned long fn, unsigned long arg)
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
-int shmobile_smp_cpu_disable(unsigned int cpu)
+bool shmobile_smp_cpu_can_disable(unsigned int cpu)
 {
-	return 0; /* Hotplug of any CPU is supported */
+	return true; /* Hotplug of any CPU is supported */
 }
 #endif
diff --git a/arch/arm/mach-shmobile/smp-r8a7790.c b/arch/arm/mach-shmobile/smp-r8a7790.c
index 930f45c..947e437 100644
--- a/arch/arm/mach-shmobile/smp-r8a7790.c
+++ b/arch/arm/mach-shmobile/smp-r8a7790.c
@@ -64,7 +64,7 @@ struct smp_operations r8a7790_smp_ops __initdata = {
 	.smp_prepare_cpus	= r8a7790_smp_prepare_cpus,
 	.smp_boot_secondary	= shmobile_smp_apmu_boot_secondary,
 #ifdef CONFIG_HOTPLUG_CPU
-	.cpu_disable		= shmobile_smp_cpu_disable,
+	.cpu_can_disable	= shmobile_smp_cpu_can_disable,
 	.cpu_die		= shmobile_smp_apmu_cpu_die,
 	.cpu_kill		= shmobile_smp_apmu_cpu_kill,
 #endif
diff --git a/arch/arm/mach-shmobile/smp-r8a7791.c b/arch/arm/mach-shmobile/smp-r8a7791.c
index 5e2d1db7..b2508c0 100644
--- a/arch/arm/mach-shmobile/smp-r8a7791.c
+++ b/arch/arm/mach-shmobile/smp-r8a7791.c
@@ -58,7 +58,7 @@ struct smp_operations r8a7791_smp_ops __initdata = {
 	.smp_prepare_cpus	= r8a7791_smp_prepare_cpus,
 	.smp_boot_secondary	= r8a7791_smp_boot_secondary,
 #ifdef CONFIG_HOTPLUG_CPU
-	.cpu_disable		= shmobile_smp_cpu_disable,
+	.cpu_can_disable	= shmobile_smp_cpu_can_disable,
 	.cpu_die		= shmobile_smp_apmu_cpu_die,
 	.cpu_kill		= shmobile_smp_apmu_cpu_kill,
 #endif
diff --git a/arch/arm/mach-shmobile/smp-sh73a0.c b/arch/arm/mach-shmobile/smp-sh73a0.c
index 2106d6b..ae7c764 100644
--- a/arch/arm/mach-shmobile/smp-sh73a0.c
+++ b/arch/arm/mach-shmobile/smp-sh73a0.c
@@ -68,7 +68,7 @@ struct smp_operations sh73a0_smp_ops __initdata = {
 	.smp_prepare_cpus	= sh73a0_smp_prepare_cpus,
 	.smp_boot_secondary	= sh73a0_boot_secondary,
 #ifdef CONFIG_HOTPLUG_CPU
-	.cpu_disable		= shmobile_smp_cpu_disable,
+	.cpu_can_disable	= shmobile_smp_cpu_can_disable,
 	.cpu_die		= shmobile_smp_scu_cpu_die,
 	.cpu_kill		= shmobile_smp_scu_cpu_kill,
 #endif