[PATCH 09/10] powerpc: Add HOTPLUG_SMT support

[Laurent Dufour]

From: Michael Ellerman <m...@ellerman.id.au>

Add support for HOTPLUG_SMT, which enables the generic sysfs SMT support
files in /sys/devices/system/cpu/smt, as well as the "nosmt" boot
parameter.

Implement the recently added hooks to allow partial SMT states, allow
any number of threads per core.

Tie the config symbol to HOTPLUG_CPU, which enables it on the major
platforms that support SMT. If there are other platforms that want the
SMT support that can be tweaked in future.

Signed-off-by: Michael Ellerman <m...@ellerman.id.au>
[ldufour: pass current SMT level to cpu_smt_set_num_threads]
[ldufour: remove topology_smt_supported]
Signed-off-by: Laurent Dufour <lduf...@linux.ibm.com>
---
 arch/powerpc/Kconfig                |  1 +
 arch/powerpc/include/asm/topology.h | 20 ++++++++++++++++++++
 arch/powerpc/kernel/smp.c           |  8 +++++++-
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 539d1f03ff42..5cf87ca10a9c 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -273,6 +273,7 @@ config PPC
        select HAVE_SYSCALL_TRACEPOINTS
        select HAVE_VIRT_CPU_ACCOUNTING
        select HAVE_VIRT_CPU_ACCOUNTING_GEN
+       select HOTPLUG_SMT                      if HOTPLUG_CPU
        select HUGETLB_PAGE_SIZE_VARIABLE       if PPC_BOOK3S_64 && HUGETLB_PAGE
        select IOMMU_HELPER                     if PPC64
        select IRQ_DOMAIN
diff --git a/arch/powerpc/include/asm/topology.h 
b/arch/powerpc/include/asm/topology.h
index 8a4d4f4d9749..7602f17d688a 100644
--- a/arch/powerpc/include/asm/topology.h
+++ b/arch/powerpc/include/asm/topology.h
@@ -143,5 +143,25 @@ static inline int cpu_to_coregroup_id(int cpu)
 #endif
 #endif
 
+#ifdef CONFIG_HOTPLUG_SMT
+#include <linux/cpu_smt.h>
+#include <asm/cputhreads.h>
+
+static inline bool topology_smt_threads_supported(unsigned int num_threads)
+{
+       return num_threads <= threads_per_core;
+}
+
+static inline bool topology_is_primary_thread(unsigned int cpu)
+{
+       return cpu == cpu_first_thread_sibling(cpu);
+}
+
+static inline bool topology_smt_thread_allowed(unsigned int cpu)
+{
+       return cpu_thread_in_core(cpu) < cpu_smt_num_threads;
+}
+#endif
+
 #endif /* __KERNEL__ */
 #endif /* _ASM_POWERPC_TOPOLOGY_H */
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 265801a3e94c..cdb77d36cdd0 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -1087,7 +1087,7 @@ static int __init init_big_cores(void)
 
 void __init smp_prepare_cpus(unsigned int max_cpus)
 {
-       unsigned int cpu;
+       unsigned int cpu, num_threads;
 
        DBG("smp_prepare_cpus\n");
 
@@ -1154,6 +1154,12 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
 
        if (smp_ops && smp_ops->probe)
                smp_ops->probe();
+
+       // Initalise the generic SMT topology support
+       num_threads = 1;
+       if (smt_enabled_at_boot)
+               num_threads = smt_enabled_at_boot;
+       cpu_smt_set_num_threads(num_threads, threads_per_core);
 }
 
 void smp_prepare_boot_cpu(void)
-- 
2.41.0