David Miller wrote:
From: Scott Wood <[EMAIL PROTECTED]>
Date: Tue, 20 May 2008 17:35:56 -0500
Alan Cox wrote:
It looks like we rely on -fno-strict-aliasing to prevent reordering
ordinary memory accesses (such as to DMA descriptors) past the I/O
DMA descriptors in main memory are dependant on cache behaviour anyway
and the dma_* operators should be the ones enforcing the needed behaviour.
What about memory obtained from dma_alloc_coherent()? We still need a
sync and a compiler barrier. The current I/O accessors have the former,
but not the latter.
The __volatile__ in the asm construct disallows movement of the
inline asm relative to statements surrounding it.
The only reason barrier() in kernel.h needs a memory clobber is
because of a bug in ancient versions of gcc. In fact, I think
that memory clobber might even be removable.
Current versions of GCC seem quite happy to move non-asm memory accesses
around a volatile asm without a memory clobber; see the test Trent posted.
-Scott
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