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Message-ID: <55241AA8.8060208@codeaurora.org>
Date: Tue, 07 Apr 2015 10:58:00 -0700
From: Stephen Boyd <sboyd@...eaurora.org>
To: Tyler Baker <tyler.baker@...aro.org>
CC: Russell King <linux@....linux.org.uk>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
Mark Rutland <mark.rutland@....com>,
Nicolas Pitre <nico@...aro.org>,
Dave Martin <Dave.Martin@....com>,
Simon Horman <horms@...ge.net.au>,
Magnus Damm <magnus.damm@...il.com>,
"linux-sh@...r.kernel.org" <linux-sh@...r.kernel.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH v4] ARM: smp: Only expose /sys/.../cpuX/online if hotpluggable
On 04/07/15 09:18, Tyler Baker wrote:
> Hi Stephen,
>
> On 6 April 2015 at 13:24, Stephen Boyd <sboyd@...eaurora.org> wrote:
>> 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@....com>
>> Cc: Nicolas Pitre <nico@...aro.org>
>> Cc: Dave Martin <Dave.Martin@....com>
>> Cc: Simon Horman <horms@...ge.net.au>
>> Cc: Magnus Damm <magnus.damm@...il.com>
>> Cc: <linux-sh@...r.kernel.org>
>> Cc: Tyler Baker <tyler.baker@...aro.org>
>> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
>> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
>> ---
>>
>> 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 | 10 ++++++++++
>> 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 +-
>> 9 files changed, 35 insertions(+), 16 deletions(-)
>>
>> diff --git a/arch/arm/common/mcpm_platsmp.c b/arch/arm/common/mcpm_platsmp.c
>> index 92e54d7c6f46..2b25b6038f66 100644
>> --- 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 18f5a554134f..e15856a1a380 100644
>> --- a/arch/arm/include/asm/smp.h
>> +++ b/arch/arm/include/asm/smp.h
>> @@ -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
>> @@ -123,4 +124,13 @@ struct of_cpu_method {
>> */
>> extern void smp_set_ops(struct smp_operations *);
>>
>> +#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 /* ifndef __ASM_ARM_SMP_H */
>> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
>> index 6c777e908a24..955d45d0f70c 100644
>> --- a/arch/arm/kernel/setup.c
>> +++ b/arch/arm/kernel/setup.c
>> @@ -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);
>> }
>>
> When I tested this patch before I only tried building
> multi_v7_defconfig (which built fine) however I've added this patch to
> my to-build branch and sent it through the CI loop. It appears that
> there quite a few build errors on the other defconfigs[0][1].
>
> ../arch/arm/kernel/setup.c: In function 'topology_init':
> ../arch/arm/kernel/setup.c:977:3: error: implicit declaration of
> function 'platform_can_hotplug_cpu'
> [-Werror=implicit-function-declaration]
> cc1: some warnings being treated as errors
> make[2]: *** [arch/arm/kernel/setup.o] Error 1
>
Ah right. asm/smp.h is not included unless CONFIG_SMP=y. We can move it
into smp_plat.h. I'll wait to see if there any other comments before
sending an update.
---8<---
diff --git a/arch/arm/include/asm/smp.h b/arch/arm/include/asm/smp.h
index e15856a1a380..2563453d7b37 100644
--- a/arch/arm/include/asm/smp.h
+++ b/arch/arm/include/asm/smp.h
@@ -124,13 +124,4 @@ struct of_cpu_method {
*/
extern void smp_set_ops(struct smp_operations *);
-#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 /* ifndef __ASM_ARM_SMP_H */
diff --git a/arch/arm/include/asm/smp_plat.h b/arch/arm/include/asm/smp_plat.h
index 0ad7d490ee6f..ebadc9956ffc 100644
--- a/arch/arm/include/asm/smp_plat.h
+++ b/arch/arm/include/asm/smp_plat.h
@@ -106,4 +106,13 @@ static inline u32 mpidr_hash_size(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
--
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