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>

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);
 }