[PATCH 3/3] spi: uniphier: introduce polling mode

[Keiji Hayashibara <hayashibara.keiji@xxxxxxxxxxxxx>]

Introduce new polling mode for short size transfer. Either the estimated
transfer time is estimated to exceed 200us, or polling loop actually exceeds
200us, it switches to irq mode.

Signed-off-by: Keiji Hayashibara <hayashibara.keiji@xxxxxxxxxxxxx>
---
 drivers/spi/spi-uniphier.c | 81 +++++++++++++++++++++++++++++++++++++---------
 1 file changed, 66 insertions(+), 15 deletions(-)

diff --git a/drivers/spi/spi-uniphier.c b/drivers/spi/spi-uniphier.c
index d40ad93..6b83b25 100644
--- a/drivers/spi/spi-uniphier.c
+++ b/drivers/spi/spi-uniphier.c
@@ -7,6 +7,7 @@
 #include <linux/bitfield.h>
 #include <linux/bitops.h>
 #include <linux/clk.h>
+#include <linux/delay.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
 #include <linux/module.h>
@@ -16,6 +17,7 @@
 #include <asm/unaligned.h>
 
 #define SSI_TIMEOUT_MS		2000
+#define SSI_POLL_TIMEOUT_US	200
 #define SSI_MAX_CLK_DIVIDER	254
 #define SSI_MIN_CLK_DIVIDER	4
 
@@ -290,21 +292,23 @@ static void uniphier_spi_recv(struct uniphier_spi_priv *priv)
 
 static void uniphier_spi_fill_tx_fifo(struct uniphier_spi_priv *priv)
 {
-	unsigned int tx_count;
+	unsigned int fifo_threshold, fill_bytes;
 	u32 val;
 
-	tx_count = DIV_ROUND_UP(priv->tx_bytes,
+	fifo_threshold = DIV_ROUND_UP(priv->rx_bytes,
 				bytes_per_word(priv->bits_per_word));
-	tx_count = min(tx_count, SSI_FIFO_DEPTH);
+	fifo_threshold = min(fifo_threshold, SSI_FIFO_DEPTH);
+
+	fill_bytes = fifo_threshold - (priv->rx_bytes - priv->tx_bytes);
 
 	/* set fifo threshold */
 	val = readl(priv->base + SSI_FC);
 	val &= ~(SSI_FC_TXFTH_MASK | SSI_FC_RXFTH_MASK);
-	val |= FIELD_PREP(SSI_FC_TXFTH_MASK, tx_count);
-	val |= FIELD_PREP(SSI_FC_RXFTH_MASK, tx_count);
+	val |= FIELD_PREP(SSI_FC_TXFTH_MASK, fifo_threshold);
+	val |= FIELD_PREP(SSI_FC_RXFTH_MASK, fifo_threshold);
 	writel(val, priv->base + SSI_FC);
 
-	while (tx_count--)
+	while (fill_bytes--)
 		uniphier_spi_send(priv);
 }
 
@@ -323,20 +327,14 @@ static void uniphier_spi_set_cs(struct spi_device *spi, bool enable)
 	writel(val, priv->base + SSI_FPS);
 }
 
-static int uniphier_spi_transfer_one(struct spi_master *master,
-				     struct spi_device *spi,
-				     struct spi_transfer *t)
+static int uniphier_spi_transfer_one_irq(struct spi_master *master,
+					 struct spi_device *spi,
+					 struct spi_transfer *t)
 {
 	struct uniphier_spi_priv *priv = spi_master_get_devdata(master);
 	struct device *dev = master->dev.parent;
 	unsigned long time_left;
 
-	/* Terminate and return success for 0 byte length transfer */
-	if (!t->len)
-		return 0;
-
-	uniphier_spi_setup_transfer(spi, t);
-
 	reinit_completion(&priv->xfer_done);
 
 	uniphier_spi_fill_tx_fifo(priv);
@@ -356,6 +354,59 @@ static int uniphier_spi_transfer_one(struct spi_master *master,
 	return priv->error;
 }
 
+static int uniphier_spi_transfer_one_poll(struct spi_master *master,
+					  struct spi_device *spi,
+					  struct spi_transfer *t)
+{
+	struct uniphier_spi_priv *priv = spi_master_get_devdata(master);
+	int loop = SSI_POLL_TIMEOUT_US * 10;
+
+	while (priv->tx_bytes) {
+		uniphier_spi_fill_tx_fifo(priv);
+
+		while ((priv->rx_bytes - priv->tx_bytes) > 0) {
+			while (!(readl(priv->base + SSI_SR) & SSI_SR_RNE)
+								&& loop--)
+				ndelay(100);
+
+			if (loop == -1)
+				goto irq_transfer;
+
+			uniphier_spi_recv(priv);
+		}
+	}
+
+	return 0;
+
+irq_transfer:
+	return uniphier_spi_transfer_one_irq(master, spi, t);
+}
+
+static int uniphier_spi_transfer_one(struct spi_master *master,
+				     struct spi_device *spi,
+				     struct spi_transfer *t)
+{
+	struct uniphier_spi_priv *priv = spi_master_get_devdata(master);
+	unsigned long threshold;
+
+	/* Terminate and return success for 0 byte length transfer */
+	if (!t->len)
+		return 0;
+
+	uniphier_spi_setup_transfer(spi, t);
+
+	/*
+	 * If the transfer operation will take longer than
+	 * SSI_POLL_TIMEOUT_US, it should use irq.
+	 */
+	threshold = DIV_ROUND_UP(SSI_POLL_TIMEOUT_US * priv->speed_hz,
+					USEC_PER_SEC * BITS_PER_BYTE);
+	if (t->len > threshold)
+		return uniphier_spi_transfer_one_irq(master, spi, t);
+	else
+		return uniphier_spi_transfer_one_poll(master, spi, t);
+}
+
 static int uniphier_spi_prepare_transfer_hardware(struct spi_master *master)
 {
 	struct uniphier_spi_priv *priv = spi_master_get_devdata(master);
-- 
2.7.4