path: root/Documentation
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authorLinus Torvalds <torvalds@linux-foundation.org>2014-12-09 17:25:00 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2014-12-09 17:25:00 -0800
commita0e4467726cd26bacb16f13d207ffcfa82ffc07d (patch)
tree98b5fcbda0cd787b07d09da90d25c87b3883c567 /Documentation
parentMerge tag 'arm64-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc (diff)
parentARM64: use GENERIC_PCI_IOMAP (diff)
Merge tag 'asm-generic-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic
Pull asm-generic asm/io.h rewrite from Arnd Bergmann: "While there normally is no reason to have a pull request for asm-generic but have all changes get merged through whichever tree needs them, I do have a series for 3.19. There are two sets of patches that change significant portions of asm/io.h, and this branch contains both in order to resolve the conflicts: - Will Deacon has done a set of patches to ensure that all architectures define {read,write}{b,w,l,q}_relaxed() functions or get them by including asm-generic/io.h. These functions are commonly used on ARM specific drivers to avoid expensive L2 cache synchronization implied by the normal {read,write}{b,w,l,q}, but we need to define them on all architectures in order to share the drivers across architectures and to enable CONFIG_COMPILE_TEST configurations for them - Thierry Reding has done an unrelated set of patches that extends the asm-generic/io.h file to the degree necessary to make it useful on ARM64 and potentially other architectures" * tag 'asm-generic-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic: (29 commits) ARM64: use GENERIC_PCI_IOMAP sparc: io: remove duplicate relaxed accessors on sparc32 ARM: sa11x0: Use void __iomem * in MMIO accessors arm64: Use include/asm-generic/io.h ARM: Use include/asm-generic/io.h asm-generic/io.h: Implement generic {read,write}s*() asm-generic/io.h: Reconcile I/O accessor overrides /dev/mem: Use more consistent data types Change xlate_dev_{kmem,mem}_ptr() prototypes ARM: ixp4xx: Properly override I/O accessors ARM: ixp4xx: Fix build with IXP4XX_INDIRECT_PCI ARM: ebsa110: Properly override I/O accessors ARC: Remove redundant PCI_IOBASE declaration documentation: memory-barriers: clarify relaxed io accessor semantics x86: io: implement dummy relaxed accessor macros for writes tile: io: implement dummy relaxed accessor macros for writes sparc: io: implement dummy relaxed accessor macros for writes powerpc: io: implement dummy relaxed accessor macros for writes parisc: io: implement dummy relaxed accessor macros for writes mn10300: io: implement dummy relaxed accessor macros for writes ...
Diffstat (limited to 'Documentation')
1 files changed, 9 insertions, 4 deletions
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index 22a969cdd476..4af4cea8cff0 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -2465,10 +2465,15 @@ functions:
Please refer to the PCI specification for more information on interactions
between PCI transactions.
- (*) readX_relaxed()
- These are similar to readX(), but are not guaranteed to be ordered in any
- way. Be aware that there is no I/O read barrier available.
+ (*) readX_relaxed(), writeX_relaxed()
+ These are similar to readX() and writeX(), but provide weaker memory
+ ordering guarantees. Specifically, they do not guarantee ordering with
+ respect to normal memory accesses (e.g. DMA buffers) nor do they guarantee
+ ordering with respect to LOCK or UNLOCK operations. If the latter is
+ required, an mmiowb() barrier can be used. Note that relaxed accesses to
+ the same peripheral are guaranteed to be ordered with respect to each
+ other.
(*) ioreadX(), iowriteX()