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authorAlexander Duyck <alexander.h.duyck@redhat.com>2014-12-11 15:01:55 -0800
committerDavid S. Miller <davem@davemloft.net>2014-12-11 21:15:05 -0500
commit8a449718414ff10b9d5559ed3e8e09c7178774f2 (patch)
tree81097c0d6949fb90e40176ddff1f4be30467b576 /arch/mips
parentc11a9009ae6a8c42a8cd69d885601e1aa6fbea04 (diff)
downloadlinux-8a449718414ff10b9d5559ed3e8e09c7178774f2.tar.bz2
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 <alexander.h.duyck@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'arch/mips')
-rw-r--r--arch/mips/include/asm/barrier.h52
1 files changed, 0 insertions, 52 deletions
diff --git a/arch/mips/include/asm/barrier.h b/arch/mips/include/asm/barrier.h
index d0101dd0575e..3d69aa829a76 100644
--- a/arch/mips/include/asm/barrier.h
+++ b/arch/mips/include/asm/barrier.h
@@ -10,58 +10,6 @@
#include <asm/addrspace.h>
-/*
- * 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"):
- *
- * <programlisting>
- * CPU 0 CPU 1
- *
- * b = 2;
- * memory_barrier();
- * p = &b; q = p;
- * read_barrier_depends();
- * d = *q;
- * </programlisting>
- *
- * 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":
- *
- * <programlisting>
- * CPU 0 CPU 1
- *
- * a = 2;
- * memory_barrier();
- * b = 3; y = b;
- * read_barrier_depends();
- * x = a;
- * </programlisting>
- *
- * 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)
#define smp_read_barrier_depends() do { } while(0)