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>

diff --git a/arch/arm/common/mcpm_platsmp.c b/arch/arm/common/mcpm_platsmp.c
index 92e54d7c6f468ebf7aa2e20b85774e885ef5aabd..2b25b6038f6694287a038f7ba5264e4f380380c9 100644 (file)
--- a/arch/arm/common/mcpm_platsmp.c
+++ b/arch/arm/common/mcpm_platsmp.c
@@ -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
 };

diff --git a/arch/arm/include/asm/smp.h b/arch/arm/include/asm/smp.h
index 2f3ac1ba6fb47329e70cfd63d40cc080edd4b63a..318ce89eeff7d040743a8de0715ab50b1cf9b55f 100644 (file)
--- a/arch/arm/include/asm/smp.h
+++ b/arch/arm/include/asm/smp.h
@@ -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

diff --git a/arch/arm/include/asm/smp_plat.h b/arch/arm/include/asm/smp_plat.h
index 993e5224d8f7eeeb09f4c2a5358a97073c67c3a6..f9080717fc88c6dd4f3e79e40a426de22100d8db 100644 (file)
--- a/arch/arm/include/asm/smp_plat.h
+++ b/arch/arm/include/asm/smp_plat.h
@@ -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

diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 36c18b73c1f4631f3882ba492dbeb1f99e9b7242..6bbec60420527b2cea13e281c01d5286f92c0083 100644 (file)
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -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);
        }
 

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 90dfbedfbfb8527b74ddcfcef125beb151f875f5..3cd846f48eafeb69e32a22e89cce6eb7957c0c09 100644 (file)
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -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.
  */

diff --git a/arch/arm/mach-shmobile/common.h b/arch/arm/mach-shmobile/common.h
index 476092b86c6e42420e2654a8d2abe8b8aa6dcaee..8d27ec546a35f4b9ee5771adc24a331006342bd1 100644 (file)
--- 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 3923e09e966d5031cab8aa82fb304305c284e9ce..b23378f3d7e1726b6f92b3cc8be0ba8264c838f7 100644 (file)
--- 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 930f45cbc08a5bb33677bbf02b5a2eb66b98d8ea..947e437cab68e3cef6f629cac6dc5ea1334494f3 100644 (file)
--- 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 5e2d1db79afa5316152d031e7bb223d1465c6e57..b2508c0d276b46d56daeac18d2e6842202b5d8f8 100644 (file)
--- 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 2106d6b76a06939238ad373486e408f7df12065f..ae7c764fd6b44a13f09ce2bc1672a288e0c83277 100644 (file)
--- 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