[PATCH 1/2] arm: Fix "NMI" backtrace for Inforce IFC6410

[daniel.thompson@linaro.org (Daniel Thompson)]

SysRq-L does not generate a backtrace from all CPUs when I test it
on my Inforce IFC6410 platform (Snapdragon 600). The stack dump code,
triggered by IPI_CPU_BACKTRACE, never runs on the other CPUs.
Eventually we hit the 10 second timeout and a subset of the expected
stack dumps on are shown on the console.

It is likely this is because SGI IDs 14 and 15 have been reserved for
use by secure world on this platform. For IFC6410 platform the code
works as expected when IPI_CPU_BACKTRACE is set to any value in the
interval 9..13.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
---
 arch/arm/kernel/smp.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index b26361355dae..78205927fcd4 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -73,7 +73,8 @@ enum ipi_msg_type {
 	IPI_CPU_STOP,
 	IPI_IRQ_WORK,
 	IPI_COMPLETION,
-	IPI_CPU_BACKTRACE = 15,
+	IPI_CPU_BACKTRACE = 13,
+	/* 14 and 15 are reserved; they do not work on some Krait CPUs */
 };
 
 static DECLARE_COMPLETION(cpu_running);
-- 
2.5.0