[RFC PATCH 3/8] powerpc/irq: don't use current_stack_pointer() in do_IRQ()

[Christophe Leroy]

Before commit 7306e83ccf5c ("powerpc: Don't use CURRENT_THREAD_INFO to
find the stack"), the current stack base address was obtained by
calling current_thread_info(). That inline function was simply masking
out the value of r1.

In that commit, it was changed to using current_stack_pointer(), which
is an heavier function as it is an outline assembly function which
cannot be inlined and which reads the content of the stack at 0(r1)

Create stack_pointer() function which returns the value of r1 and use
it instead.

Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>
Fixes: 7306e83ccf5c ("powerpc: Don't use CURRENT_THREAD_INFO to find the stack")
---
 arch/powerpc/include/asm/reg.h | 8 ++++++++
 arch/powerpc/kernel/irq.c      | 2 +-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 1aa46dff0957..bc14fca9b13b 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -1466,6 +1466,14 @@ static inline void update_power8_hid0(unsigned long hid0)
 	 */
 	asm volatile("sync; mtspr %0,%1; isync":: "i"(SPRN_HID0), "r"(hid0));
 }
+
+static __always_inline unsigned long stack_pointer(void)
+{
+	register unsigned long r1 asm("r1");
+
+	return r1;
+}
+
 #endif /* __ASSEMBLY__ */
 #endif /* __KERNEL__ */
 #endif /* _ASM_POWERPC_REG_H */
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 4690e5270806..410accba865d 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -680,7 +680,7 @@ void do_IRQ(struct pt_regs *regs)
 	void *cursp, *irqsp, *sirqsp;
 
 	/* Switch to the irq stack to handle this */
-	cursp = (void *)(current_stack_pointer() & ~(THREAD_SIZE - 1));
+	cursp = (void *)(stack_pointer() & ~(THREAD_SIZE - 1));
 	irqsp = hardirq_ctx[raw_smp_processor_id()];
 	sirqsp = softirq_ctx[raw_smp_processor_id()];
 
-- 
2.13.3