From 41195d236e84458bebd4fdc218610a92231ac791 Mon Sep 17 00:00:00 2001 From: Vineet Gupta Date: Fri, 18 Jan 2013 15:12:23 +0530 Subject: ARC: SMP support ARC common code to enable a SMP system + ISS provided SMP extensions. ARC700 natively lacks SMP support, hence some of the core features are are only enabled if SoCs have the necessary h/w pixie-dust. This includes: -Inter Processor Interrupts (IPI) -Cache coherency -load-locked/store-conditional ... The low level exception handling would be completely broken in SMP because we don't have hardware assisted stack switching. Thus a fair bit of this code is repurposing the MMU_SCRATCH reg for event handler prologues to keep them re-entrant. Many thanks to Rajeshwar Ranga for his initial "major" contributions to SMP Port (back in 2008), and to Noam Camus and Gilad Ben-Yossef for help with resurrecting that in 3.2 kernel (2012). Note that this platform code is again singleton design pattern - so multiple SMP platforms won't build at the moment - this deficiency is addressed in subsequent patches within this series. Signed-off-by: Vineet Gupta Cc: Arnd Bergmann Cc: Thomas Gleixner Cc: Rajeshwar Ranga Cc: Noam Camus Cc: Gilad Ben-Yossef --- arch/arc/include/asm/processor.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'arch/arc/include/asm/processor.h') diff --git a/arch/arc/include/asm/processor.h b/arch/arc/include/asm/processor.h index b7b155610067..5f26b2c1cba0 100644 --- a/arch/arc/include/asm/processor.h +++ b/arch/arc/include/asm/processor.h @@ -58,7 +58,15 @@ unsigned long thread_saved_pc(struct task_struct *t); /* Prepare to copy thread state - unlazy all lazy status */ #define prepare_to_copy(tsk) do { } while (0) +/* + * A lot of busy-wait loops in SMP are based off of non-volatile data otherwise + * get optimised away by gcc + */ +#ifdef CONFIG_SMP +#define cpu_relax() __asm__ __volatile__ ("" : : : "memory") +#else #define cpu_relax() do { } while (0) +#endif #define copy_segments(tsk, mm) do { } while (0) #define release_segments(mm) do { } while (0) -- cgit v1.2.3