[RFC PATCH 1/2] dma-direction: Add DMA_DIR_COMPAT() macro to test direction compability

[Leonardo Bras]

Given a existing mapping with 'current' direction, and a 'wanted'
direction for using that mapping, check if 'wanted' is satisfied by
'current'.

current			accepts
DMA_BIDIRECTIONAL	DMA_BIDIRECTIONAL, DMA_TO_DEVICE,
			DMA_FROM_DEVICE, DMA_NONE
DMA_TO_DEVICE		DMA_TO_DEVICE, DMA_NONE
DMA_FROM_DEVICE		DMA_FROM_DEVICE, DMA_NONE
DMA_NONE		DMA_NONE

This macro is useful for checking if a DMA mapping can be reused.

Signed-off-by: Leonardo Bras <leobras.c at gmail.com>
---
 include/linux/dma-direction.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/dma-direction.h b/include/linux/dma-direction.h
index 9c96e30e6a0b..caf3943a21f4 100644
--- a/include/linux/dma-direction.h
+++ b/include/linux/dma-direction.h
@@ -9,4 +9,7 @@ enum dma_data_direction {
 	DMA_NONE = 3,
 };
 
+/* Checks if wanted direction is satisfied by current mapping direction*/
+#define DMA_DIR_COMPAT(current, wanted)	(((current) & ~(wanted)) == 0)
+
 #endif
-- 
2.25.4