dmaengine: Add helper function to convert direction value to text

dmaengine_get_direction_text() can be useful when the direction is printed
out. The text is easier to comprehend than the number.
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Link: https://lore.kernel.org/r/20191223110458.30766-7-peter.ujfalusi@ti.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

include/linux/dmaengine.h

@@ -1545,4 +1545,23 @@ static inline struct dma_chan
 
 	return __dma_request_channel(mask, fn, fn_param, NULL);
 }
+
+static inline char *
+dmaengine_get_direction_text(enum dma_transfer_direction dir)
+{
+	switch (dir) {
+	case DMA_DEV_TO_MEM:
+		return "DEV_TO_MEM";
+	case DMA_MEM_TO_DEV:
+		return "MEM_TO_DEV";
+	case DMA_MEM_TO_MEM:
+		return "MEM_TO_MEM";
+	case DMA_DEV_TO_DEV:
+		return "DEV_TO_DEV";
+	default:
+		break;
+	}
+
+	return "invalid";
+}
 #endif /* DMAENGINE_H */