[PATCH v5 22/33] spi: dw: Speed up transfer loops

[Sean Anderson]

The transfer loops are very tight on some platforms (especially on higher
speeds). If we don't read/write fast enough we can run into over-/under-
flow problems. This patch removes several divisions and log statements,
and simplifies the read logic.

Signed-off-by: Sean Anderson <sean...@gmail.com>
---

Changes in v5:
- New

 drivers/spi/designware_spi.c | 29 +++++++++--------------------
 1 file changed, 9 insertions(+), 20 deletions(-)

diff --git a/drivers/spi/designware_spi.c b/drivers/spi/designware_spi.c
index 38c24fe550..613eb0d0e6 100644
--- a/drivers/spi/designware_spi.c
+++ b/drivers/spi/designware_spi.c
@@ -304,7 +304,7 @@ static inline u32 tx_max(struct dw_spi_priv *priv)
 {
        u32 tx_left, tx_room, rxtx_gap;
 
-       tx_left = (priv->tx_end - priv->tx) / (priv->bits_per_word >> 3);
+       tx_left = priv->tx_end - priv->tx;
        tx_room = priv->fifo_len - dw_read(priv, DW_SPI_TXFLR);
 
        /*
@@ -315,8 +315,7 @@ static inline u32 tx_max(struct dw_spi_priv *priv)
         * shift registers. So a control from sw point of
         * view is taken.
         */
-       rxtx_gap = ((priv->rx_end - priv->rx) - (priv->tx_end - priv->tx)) /
-               (priv->bits_per_word >> 3);
+       rxtx_gap = ((priv->rx_end - priv->rx) - (priv->tx_end - priv->tx));
 
        return min3(tx_left, tx_room, (u32)(priv->fifo_len - rxtx_gap));
 }
@@ -324,7 +323,7 @@ static inline u32 tx_max(struct dw_spi_priv *priv)
 /* Return the max entries we should read out of rx fifo */
 static inline u32 rx_max(struct dw_spi_priv *priv)
 {
-       u32 rx_left = (priv->rx_end - priv->rx) / (priv->bits_per_word >> 3);
+       u32 rx_left = priv->rx_end - priv->rx;
 
        return min_t(u32, rx_left, dw_read(priv, DW_SPI_RXFLR));
 }
@@ -336,15 +335,10 @@ static void dw_writer(struct dw_spi_priv *priv)
 
        while (max--) {
                /* Set the tx word if the transfer's original "tx" is not null 
*/
-               if (priv->tx_end - priv->len) {
-                       if (priv->bits_per_word == 8)
-                               txw = *(u8 *)(priv->tx);
-                       else
-                               txw = *(u16 *)(priv->tx);
-               }
+               if (priv->tx_end - priv->len)
+                       txw = *(u8 *)(priv->tx);
                dw_write(priv, DW_SPI_DR, txw);
-               debug("%s: tx=0x%02x\n", __func__, txw);
-               priv->tx += priv->bits_per_word >> 3;
+               priv->tx++;
        }
 }
 
@@ -355,16 +349,11 @@ static void dw_reader(struct dw_spi_priv *priv)
 
        while (max--) {
                rxw = dw_read(priv, DW_SPI_DR);
-               debug("%s: rx=0x%02x\n", __func__, rxw);
 
                /* Care about rx if the transfer's original "rx" is not null */
-               if (priv->rx_end - priv->len) {
-                       if (priv->bits_per_word == 8)
-                               *(u8 *)(priv->rx) = rxw;
-                       else
-                               *(u16 *)(priv->rx) = rxw;
-               }
-               priv->rx += priv->bits_per_word >> 3;
+               if (priv->rx_end - priv->len)
+                       *(u8 *)(priv->rx) = rxw;
+               priv->rx++;
        }
 }
 
-- 
2.25.0