From 8a449718414ff10b9d5559ed3e8e09c7178774f2 Mon Sep 17 00:00:00 2001 From: Alexander Duyck Date: Thu, 11 Dec 2014 15:01:55 -0800 Subject: arch: Cleanup read_barrier_depends() and comments This patch is meant to cleanup the handling of read_barrier_depends and smp_read_barrier_depends. In multiple spots in the kernel headers read_barrier_depends is defined as "do {} while (0)", however we then go into the SMP vs non-SMP sections and have the SMP version reference read_barrier_depends, and the non-SMP define it as yet another empty do/while. With this commit I went through and cleaned out the duplicate definitions and reduced the number of definitions down to 2 per header. In addition I moved the 50 line comments for the macro from the x86 and mips headers that defined it as an empty do/while to those that were actually defining the macro, alpha and blackfin. Signed-off-by: Alexander Duyck Signed-off-by: David S. Miller --- arch/x86/include/asm/barrier.h | 59 +++--------------------------------------- 1 file changed, 3 insertions(+), 56 deletions(-) (limited to 'arch/x86/include/asm/barrier.h') diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h index 0f4460b5636d..5238000285c1 100644 --- a/arch/x86/include/asm/barrier.h +++ b/arch/x86/include/asm/barrier.h @@ -24,60 +24,6 @@ #define wmb() asm volatile("sfence" ::: "memory") #endif -/** - * read_barrier_depends - Flush all pending reads that subsequents reads - * depend on. - * - * No data-dependent reads from memory-like regions are ever reordered - * over this barrier. All reads preceding this primitive are guaranteed - * to access memory (but not necessarily other CPUs' caches) before any - * reads following this primitive that depend on the data return by - * any of the preceding reads. This primitive is much lighter weight than - * rmb() on most CPUs, and is never heavier weight than is - * rmb(). - * - * These ordering constraints are respected by both the local CPU - * and the compiler. - * - * Ordering is not guaranteed by anything other than these primitives, - * not even by data dependencies. See the documentation for - * memory_barrier() for examples and URLs to more information. - * - * For example, the following code would force ordering (the initial - * value of "a" is zero, "b" is one, and "p" is "&a"): - * - * - * CPU 0 CPU 1 - * - * b = 2; - * memory_barrier(); - * p = &b; q = p; - * read_barrier_depends(); - * d = *q; - * - * - * because the read of "*q" depends on the read of "p" and these - * two reads are separated by a read_barrier_depends(). However, - * the following code, with the same initial values for "a" and "b": - * - * - * CPU 0 CPU 1 - * - * a = 2; - * memory_barrier(); - * b = 3; y = b; - * read_barrier_depends(); - * x = a; - * - * - * does not enforce ordering, since there is no data dependency between - * the read of "a" and the read of "b". Therefore, on some CPUs, such - * as Alpha, "y" could be set to 3 and "x" to 0. Use rmb() - * in cases like this where there are no data dependencies. - **/ - -#define read_barrier_depends() do { } while (0) - #ifdef CONFIG_SMP #define smp_mb() mb() #ifdef CONFIG_X86_PPRO_FENCE @@ -86,16 +32,17 @@ # define smp_rmb() barrier() #endif #define smp_wmb() barrier() -#define smp_read_barrier_depends() read_barrier_depends() #define set_mb(var, value) do { (void)xchg(&var, value); } while (0) #else /* !SMP */ #define smp_mb() barrier() #define smp_rmb() barrier() #define smp_wmb() barrier() -#define smp_read_barrier_depends() do { } while (0) #define set_mb(var, value) do { var = value; barrier(); } while (0) #endif /* SMP */ +#define read_barrier_depends() do { } while (0) +#define smp_read_barrier_depends() do { } while (0) + #if defined(CONFIG_X86_PPRO_FENCE) /* -- cgit v1.2.3