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When the coherent DMA buffers are mapped as Normal Non-cacheable (ARM_DMA_MEM_BUFFERABLE enabled), buffer accesses are no longer ordered with Device memory accesses causing failures in device drivers that do not use the mandatory memory barriers before starting a DMA transfer. LKML discussions led to the conclusion that such barriers have to be added to the I/O accessors: http://thread.gmane.org/gmane.linux.kernel/683509/focus=686153 http://thread.gmane.org/gmane.linux.ide/46414 http://thread.gmane.org/gmane.linux.kernel.cross-arch/5250 This patch introduces a wmb() barrier to the write*() I/O accessors to handle the situations where Normal Non-cacheable writes are still in the processor (or L2 cache controller) write buffer before a DMA transfer command is issued. For the read*() accessors, a rmb() is introduced after the I/O to avoid speculative loads where the driver polls for a DMA transfer ready bit. Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> |
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