spi/dw_spi: change poll mode transfer from byte ops to batch ops

Current poll transfer will read/write one word, then wait till the
hw is non-busy, it's not efficient. This patch will try to read/write
as many words as permitted by hardware FIFO depth.

Signed-off-by: Alek Du <alek.du@intel.com>
Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

diff --git a/drivers/spi/dw_spi.c b/drivers/spi/dw_spi.c
index d3aaf8d..7a2a722 100644 (file)
--- a/drivers/spi/dw_spi.c
+++ b/drivers/spi/dw_spi.c
@@ -160,6 +160,37 @@ static inline void mrst_spi_debugfs_remove(struct dw_spi *dws)
 }
 #endif /* CONFIG_DEBUG_FS */
 
+/* Return the max entries we can fill into tx fifo */
+static inline u32 tx_max(struct dw_spi *dws)
+{
+       u32 tx_left, tx_room, rxtx_gap;
+
+       tx_left = (dws->tx_end - dws->tx) / dws->n_bytes;
+       tx_room = dws->fifo_len - dw_readw(dws, txflr);
+
+       /*
+        * Another concern is about the tx/rx mismatch, we
+        * though to use (dws->fifo_len - rxflr - txflr) as
+        * one maximum value for tx, but it doesn't cover the
+        * data which is out of tx/rx fifo and inside the
+        * shift registers. So a control from sw point of
+        * view is taken.
+        */
+       rxtx_gap =  ((dws->rx_end - dws->rx) - (dws->tx_end - dws->tx))
+                       / dws->n_bytes;
+
+       return min3(tx_left, tx_room, (u32) (dws->fifo_len - rxtx_gap));
+}
+
+/* Return the max entries we should read out of rx fifo */
+static inline u32 rx_max(struct dw_spi *dws)
+{
+       u32 rx_left = (dws->rx_end - dws->rx) / dws->n_bytes;
+
+       return min(rx_left, (u32)dw_readw(dws, rxflr));
+}
+
+
 static void wait_till_not_busy(struct dw_spi *dws)
 {
        unsigned long end = jiffies + 1 + usecs_to_jiffies(5000);
@@ -175,33 +206,30 @@ static void wait_till_not_busy(struct dw_spi *dws)
 
 static int dw_writer(struct dw_spi *dws)
 {
+       u32 max = tx_max(dws);
        u16 txw = 0;
 
-       if (!(dw_readw(dws, sr) & SR_TF_NOT_FULL)
-               || (dws->tx == dws->tx_end))
-               return 0;
-
-       /* Set the tx word if the transfer's original "tx" is not null */
-       if (dws->tx_end - dws->len) {
-               if (dws->n_bytes == 1)
-                       txw = *(u8 *)(dws->tx);
-               else
-                       txw = *(u16 *)(dws->tx);
+       while (max--) {
+               /* Set the tx word if the transfer's original "tx" is not null */
+               if (dws->tx_end - dws->len) {
+                       if (dws->n_bytes == 1)
+                               txw = *(u8 *)(dws->tx);
+                       else
+                               txw = *(u16 *)(dws->tx);
+               }
+               dw_writew(dws, dr, txw);
+               dws->tx += dws->n_bytes;
        }
 
-       dw_writew(dws, dr, txw);
-       dws->tx += dws->n_bytes;
-
-       wait_till_not_busy(dws);
        return 1;
 }
 
 static int dw_reader(struct dw_spi *dws)
 {
+       u32 max = rx_max(dws);
        u16 rxw;
 
-       while ((dw_readw(dws, sr) & SR_RF_NOT_EMPT)
-               && (dws->rx < dws->rx_end)) {
+       while (max--) {
                rxw = dw_readw(dws, dr);
                /* Care rx only if the transfer's original "rx" is not null */
                if (dws->rx_end - dws->len) {
@@ -213,7 +241,6 @@ static int dw_reader(struct dw_spi *dws)
                dws->rx += dws->n_bytes;
        }
 
-       wait_till_not_busy(dws);
        return dws->rx == dws->rx_end;
 }
 
@@ -368,13 +395,11 @@ static irqreturn_t dw_spi_irq(int irq, void *dev_id)
 /* Must be called inside pump_transfers() */
 static void poll_transfer(struct dw_spi *dws)
 {
-       while (dw_writer(dws))
+       do {
+               dw_writer(dws);
                dw_reader(dws);
-       /*
-        * There is a possibility that the last word of a transaction
-        * will be lost if data is not ready. Re-read to solve this issue.
-        */
-       dw_reader(dws);
+               cpu_relax();
+       } while (dws->rx_end > dws->rx);
 
        dw_spi_xfer_done(dws);
 }