FAILED: patch "[PATCH] powerpc/pseries: Always enable CONFIG_HOTPLUG_CPU on PSERIES" failed to apply to 3.9-stable tree

Please find the 3.9 backport below. Thank you!

Regards,
Srivatsa S. Bhat

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From: Srivatsa S. Bhat <[email protected]>
Subject: [PATCH] powerpc/pseries: Always enable CONFIG_HOTPLUG_CPU on PSERIES SMP

commit f274ef8747d3be649bba8708696fb31cb00fa75a upstream.

Adam Lackorzynski reported the following build failure on !CONFIG_HOTPLUG_CPU configuration:

CC arch/powerpc/kernel/rtas.o
arch/powerpc/kernel/rtas.c: In function ‘rtas_cpu_state_change_mask’:
arch/powerpc/kernel/rtas.c:843:4: error: implicit declaration of function ‘cpu_down’ [-Werror=implicit-function-declaration]
cc1: all warnings being treated as errors
make[1]: *** [arch/powerpc/kernel/rtas.o] Error 1
make: *** [arch/powerpc/kernel] Error 2

The build fails because cpu_down() is defined only under CONFIG_HOTPLUG_CPU.

Looking further, the mobility code in pseries is one of the call-sites which uses rtas_ibm_suspend_me(), which in turn calls rtas_cpu_state_change_mask(). And the mobility code is unconditionally compiled-in (it does not fall under any Kconfig option). And commit 120496ac (powerpc: Bring all threads online prior to migration/hibernation) which introduced this build regression is critical for the proper functioning of the migration code. So it appears that the only solution to this problem is to enable CONFIG_HOTPLUG_CPU if SMP is enabled on PPC_PSERIES platforms. So make that change in the Kconfig.

---

 arch/powerpc/platforms/pseries/Kconfig |    2 ++
 1 file changed, 2 insertions(+)

index 9a0941b..b9fd0d3 100644
@@ -18,6 +18,8 @@ config PPC_PSERIES
 	select PPC_PCI_CHOICE if EXPERT
 	select ZLIB_DEFLATE
 	select PPC_DOORBELL
+	select HOTPLUG if SMP
+	select HOTPLUG_CPU if SMP
 	default y
 
 config PPC_SPLPAR