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Revision 7a0bac4d

ID7a0bac4da9c6a2e36d388412f3b4074b10429e8e

Added by Benjamin Herrenschmidt almost 8 years ago

Add a memory barrier to DMA functions

The emulated devices can run simultaneously with the guest, so
we need to be careful with ordering of load and stores done by
them to the guest system memory, which need to be observed in
the right order by the guest operating system.

This adds a barrier call to the basic DMA read/write ops which
is currently implemented as a smp_mb(), but could be later
improved for more fine grained control of barriers.

Additionally, a _relaxed() variant of the accessors is provided
to easily convert devices who would be performance sensitive
and negatively impacted by the change.

Signed-off-by: Benjamin Herrenschmidt <>
Signed-off-by: Anthony Liguori <>

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