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 <jan.nikitenko@gmail.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 10 deletions

diff --git a/drivers/spi/au1550_spi.c b/drivers/spi/au1550_spi.c
index 87b73e0169c5..b02f25c702fd 100644
--- a/drivers/spi/au1550_spi.c
+++ b/drivers/spi/au1550_spi.c
@@ -369,10 +369,23 @@ static int au1550_spi_dma_txrxb(struct spi_device *spi, struct spi_transfer *t)
         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,
@@ -396,15 +409,8 @@ static int au1550_spi_dma_txrxb(struct spi_device *spi, struct spi_transfer *t)
                 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;