powerpc/powernv: Ignore smt-enabled on Power8 and later

Starting with POWER8, the subcore logic relies on all threads of a core
being booted so that they can participate in split mode switches. So on
those machines we ignore the smt_enabled_at_boot setting (smt-enabled on
the kernel command line).

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
[mpe: Update comment and change log to be more precise]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 15 insertions, 1 deletions

diff --git a/arch/powerpc/platforms/powernv/smp.c b/arch/powerpc/platforms/powernv/smp.c
index 6c551a28e899..fc34025ef822 100644
--- a/arch/powerpc/platforms/powernv/smp.c
+++ b/arch/powerpc/platforms/powernv/smp.c
@@ -209,13 +209,27 @@ static void pnv_smp_cpu_kill_self(void)
 
 #endif /* CONFIG_HOTPLUG_CPU */
 
+static int pnv_cpu_bootable(unsigned int nr)
+{
+        /*
+         * Starting with POWER8, the subcore logic relies on all threads of a
+         * core being booted so that they can participate in split mode
+         * switches. So on those machines we ignore the smt_enabled_at_boot
+         * setting (smt-enabled on the kernel command line).
+         */
+        if (cpu_has_feature(CPU_FTR_ARCH_207S))
+                return 1;
+
+        return smp_generic_cpu_bootable(nr);
+}
+
 static struct smp_ops_t pnv_smp_ops = {
         .message_pass   = smp_muxed_ipi_message_pass,
         .cause_ipi      = NULL, /* Filled at runtime by xics_smp_probe() */
         .probe          = xics_smp_probe,
         .kick_cpu       = pnv_smp_kick_cpu,
         .setup_cpu      = pnv_smp_setup_cpu,
-        .cpu_bootable   = smp_generic_cpu_bootable,
+        .cpu_bootable   = pnv_cpu_bootable,
 #ifdef CONFIG_HOTPLUG_CPU
         .cpu_disable    = pnv_smp_cpu_disable,
         .cpu_die        = generic_cpu_die,