[PATCH v2] MIPS: Fix minimum alignment requirement of IRQ stack

[Matt Redfearn <matt.redfearn@imgtec.com>]

Commit db8466c581cc ("MIPS: IRQ Stack: Unwind IRQ stack onto task
stack") erroneously set the initial stack pointer of the IRQ stack to a
value with a 4 byte alignment. The MIPS32 ABI requires that the minimum
stack alignment is 8 byte, and the MIPS64 ABIs(n32/n64) require 16 byte
minimum alignment. Fix IRQ_STACK_START such that it leaves space for the
dummy stack frame (containing interrupted task kernel stack pointer)
while also meeting minimum alignment requirements.

Fixes: db8466c581cc ("MIPS: IRQ Stack: Unwind IRQ stack onto task stack")
Reported-by: Darius Ivanauskas <dasilt@yahoo.com>
Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
---

Changes in v2:
Don't include asm/asm.h since the definitions in it lead to breakage
when it pollutes the C namespace (thanks kbuild test robot!)

 arch/mips/include/asm/irq.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/include/asm/irq.h b/arch/mips/include/asm/irq.h
index ddd1c918103b..c5d351786416 100644
--- a/arch/mips/include/asm/irq.h
+++ b/arch/mips/include/asm/irq.h
@@ -18,7 +18,7 @@
 #include <irq.h>
 
 #define IRQ_STACK_SIZE			THREAD_SIZE
-#define IRQ_STACK_START			(IRQ_STACK_SIZE - sizeof(unsigned long))
+#define IRQ_STACK_START			(IRQ_STACK_SIZE - 16)
 
 extern void *irq_stack[NR_CPUS];
 
-- 
2.7.4