ARM: 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 <[email protected]>

Cc Nicolas Pitre <[email protected]>

Cc Dave Martin <[email protected]>

Acked-by Simon Horman <[email protected]> [shmobile portion]

Tested-by Simon Horman <[email protected]>

Cc Magnus Damm <[email protected]>

Cc <[email protected]>

Cc Tyler Baker <[email protected]>

Cc Geert Uytterhoeven <[email protected]>

Signed-off-by Stephen Boyd <[email protected]>

---

Changes since v4:
* Fix build error on !SMP (Tyler Baker)
* Picked up Simon's ack/tested-by

Changes since v3:
* Return bool instead of int from 'cpu_can_disable' op

Changes since v2:
* Left cpu_disable op in place
* Split out shmobile function deletion

 arch/arm/common/mcpm_platsmp.c       | 12 ++++--------
 arch/arm/include/asm/smp.h           |  1 +
 arch/arm/include/asm/smp_plat.h      |  9 +++++++++
 arch/arm/kernel/setup.c              |  2 +-
 arch/arm/kernel/smp.c                | 15 ++++++++++++++-
 arch/arm/mach-shmobile/common.h      |  2 +-
 arch/arm/mach-shmobile/platsmp.c     |  4 ++--
 arch/arm/mach-shmobile/smp-r8a7790.c |  2 +-
 arch/arm/mach-shmobile/smp-r8a7791.c |  2 +-
 arch/arm/mach-shmobile/smp-sh73a0.c  |  2 +-
 10 files changed, 35 insertions(+), 16 deletions(-)

arch/arm/common/mcpm_platsmp.c +4 -8

index 92e54d7c6f46..2b25b6038f66 100644
@@ -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

index 18f5a554134f..2563453d7b37 100644
@@ -104,6 +104,7 @@ 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

index 993e5224d8f7..f9080717fc88 100644
@@ -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

index 6c777e908a24..955d45d0f70c 100644
@@ -992,7 +992,7 @@ 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

index cca5b8758185..8c834ecc09db 100644
@@ -173,13 +173,26 @@ 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.
  */

arch/arm/mach-shmobile/common.h +1 -1

index afc60bad6fd6..f2c4bf437ea7 100644
@@ -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_invalidate_start(void);
 extern void shmobile_boot_scu(void);
 extern void shmobile_smp_scu_prepare_cpus(unsigned int max_cpus);

arch/arm/mach-shmobile/platsmp.c +2 -2

index 3923e09e966d..b23378f3d7e1 100644
@@ -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

arch/arm/mach-shmobile/smp-r8a7790.c +1 -1

index 930f45cbc08a..947e437cab68 100644
@@ -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

arch/arm/mach-shmobile/smp-r8a7791.c +1 -1

index 5e2d1db79afa..b2508c0d276b 100644
@@ -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

arch/arm/mach-shmobile/smp-sh73a0.c +1 -2

index 2106d6b76a06..ae7c764fd6b4 100644
@@ -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
--

The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project

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 <[email protected]>

Cc Nicolas Pitre <[email protected]>

Cc Dave Martin <[email protected]>

Acked-by Simon Horman <[email protected]> [shmobile portion]

Tested-by Simon Horman <[email protected]>

Cc Magnus Damm <[email protected]>

Cc <[email protected]>

Cc Tyler Baker <[email protected]>

Cc Geert Uytterhoeven <[email protected]>

Signed-off-by Stephen Boyd <[email protected]>

Quoted 21 lines · Stephen Boyd

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.

Quoted 10 lines

Cc Mark Rutland <[email protected]>

Cc Nicolas Pitre <[email protected]>

Cc Dave Martin <[email protected]>

Acked-by Simon Horman <[email protected]> [shmobile portion]

Tested-by Simon Horman <[email protected]>

Cc Magnus Damm <[email protected]>

Cc <[email protected]>

Cc Tyler Baker <[email protected]>

Cc Geert Uytterhoeven <[email protected]>

Signed-off-by Stephen Boyd <[email protected]>

Let's see some more acks for this...

Quoted 11 lines · Russell King - ARM Linux

Quoted 10 lines · Stephen Boyd

Cc Mark Rutland <[email protected]>

Cc Nicolas Pitre <[email protected]>

Cc Dave Martin <[email protected]>

Acked-by Simon Horman <[email protected]> [shmobile portion]

Tested-by Simon Horman <[email protected]>

Cc Magnus Damm <[email protected]>

Cc <[email protected]>

Cc Tyler Baker <[email protected]>

Cc Geert Uytterhoeven <[email protected]>

Signed-off-by Stephen Boyd <[email protected]>

Quoted 2 lines

Let's see some more acks for this...

Nobody else has acked this so far. Shall I put it in the patch tracker now? Or is there someone more specific we need an ack from?

Quoted 15 lines · Stephen Boyd

Quoted 13 lines · Russell King - ARM Linux

Quoted 10 lines · Stephen Boyd

Cc Mark Rutland <[email protected]>

Cc Nicolas Pitre <[email protected]>

Cc Dave Martin <[email protected]>

Acked-by Simon Horman <[email protected]> [shmobile portion]

Tested-by Simon Horman <[email protected]>

Cc Magnus Damm <[email protected]>

Cc <[email protected]>

Cc Tyler Baker <[email protected]>

Cc Geert Uytterhoeven <[email protected]>

Signed-off-by Stephen Boyd <[email protected]>

Let's see some more acks for this...

Quoted 2 lines

Nobody else has acked this so far. Shall I put it in the patch tracker now? Or is there someone more specific we need an ack from?

I guess if people haven't responded by now, they're never going to respond, and I guess we take their non-response as tacit approval for the change.

Maybe we ought to have tacit-acked-by: which we can add when someones been Cc'd and hasn't responded. :)

Quoted 32 lines · Russell King - ARM Linux

Quoted 31 lines · Stephen Boyd

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 <[email protected]>

Cc Nicolas Pitre <[email protected]>

Cc Dave Martin <[email protected]>

Acked-by Simon Horman <[email protected]> [shmobile portion]

Tested-by Simon Horman <[email protected]>

Cc Magnus Damm <[email protected]>

Cc <[email protected]>

Cc Tyler Baker <[email protected]>

Cc Geert Uytterhoeven <[email protected]>

Signed-off-by Stephen Boyd <[email protected]>

Quoted 2 lines

Let's see some more acks for this...

Nobody else has acked this so far. Shall I put it in the patch tracker now? Or is there someone more specific we need an ack from?

arch/arm/mach-shmobile/common.h +2 -1

index 476092b86c6e..f2c4bf437ea7 100644
@@ -13,7 +13,8 @@ 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_invalidate_start(void);
 

which your original patch did not include. The tree I'm applying to (-rc1) contains:

extern int shmobile_smp_cpu_disable(unsigned int cpu); extern void shmobile_invalidate_start(void);

there. Hence git quite rightfully declines to apply the patch.

Quoted 15 lines · Russell King - ARM Linux

arch/arm/mach-shmobile/common.h +2 -1

index 476092b86c6e..f2c4bf437ea7 100644
@@ -13,7 +13,8 @@ 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_invalidate_start(void);
 

which your original patch did not include. The tree I'm applying to (-rc1) contains:

Quoted 5 lines

extern int shmobile_smp_cpu_disable(unsigned int cpu); extern void shmobile_invalidate_start(void);

there. Hence git quite rightfully declines to apply the patch.

Thanks. Fixed.

Quoted 19 lines · Stephen Boyd

Quoted 18 lines · Russell King - ARM Linux

arch/arm/mach-shmobile/common.h +2 -1

index 476092b86c6e..f2c4bf437ea7 100644
@@ -13,7 +13,8 @@ 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_invalidate_start(void);
 

which your original patch did not include. The tree I'm applying to (-rc1) contains:

extern int shmobile_smp_cpu_disable(unsigned int cpu); extern void shmobile_invalidate_start(void);

Quoted 4 lines

Quoted 2 lines

there. Hence git quite rightfully declines to apply the patch.

Thanks. Fixed.

Sorry I just noticed that you applied 8392/1 instead of 8392/2 from the patch tracker. So shmobile_invalidate_start() came back.

I thought it would automatically supersede the previous patch but it looks like it just sticks around?