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>

1 files changed, 48 insertions, 23 deletions

diff --git a/drivers/spi/dw_spi.c b/drivers/spi/dw_spi.c
index d3aaf8db86cc..7a2a72268f0a 100644
--- 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);
 }