spi: au1550_spi full duplex dma fix

Fix unsafe order in dma mapping operation: always flush data from the
cache *BEFORE* invalidating it, to allow full duplex transfers where the
same buffer may be used for both writes and reads. Tested with mmc-spi.

Signed-off-by: Jan Nikitenko <[e-mail]>
Signed-off-by: David Brownell <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/spi/au1550_spi.c

···
 	dma_rx_addr = t->rx_dma;
 
 	/*
-	 * check if buffers are already dma mapped, map them otherwise
+	 * check if buffers are already dma mapped, map them otherwise:
+	 * - first map the TX buffer, so cache data gets written to memory
+	 * - then map the RX buffer, so that cache entries (with
+	 *   soon-to-be-stale data) get removed
 	 * use rx buffer in place of tx if tx buffer was not provided
 	 * use temp rx buffer (preallocated or realloc to fit) for rx dma
 	 */
+	if (t->tx_buf) {
+		if (t->tx_dma == 0) {	/* if DMA_ADDR_INVALID, map it */
+			dma_tx_addr = dma_map_single(hw->dev,
+					(void *)t->tx_buf,
+					t->len, DMA_TO_DEVICE);
+			if (dma_mapping_error(hw->dev, dma_tx_addr))
+				dev_err(hw->dev, "tx dma map error\n");
+		}
+	}
+
 	if (t->rx_buf) {
 		if (t->rx_dma == 0) {	/* if DMA_ADDR_INVALID, map it */
 			dma_rx_addr = dma_map_single(hw->dev,
···
 		dma_sync_single_for_device(hw->dev, dma_rx_addr,
 			t->len, DMA_FROM_DEVICE);
 	}
-	if (t->tx_buf) {
-		if (t->tx_dma == 0) {	/* if DMA_ADDR_INVALID, map it */
-			dma_tx_addr = dma_map_single(hw->dev,
-					(void *)t->tx_buf,
-					t->len, DMA_TO_DEVICE);
-			if (dma_mapping_error(hw->dev, dma_tx_addr))
-				dev_err(hw->dev, "tx dma map error\n");
-		}
-	} else {
+
+	if (!t->tx_buf) {
 		dma_sync_single_for_device(hw->dev, dma_rx_addr,
 				t->len, DMA_BIDIRECTIONAL);
 		hw->tx = hw->rx;