spi: uniphier: introduce polling mode

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@socionext.com>
Link: https://lore.kernel.org/r/1567488661-11428-4-git-send-email-hayashibara.keiji@socionext.com
Signed-off-by: Mark Brown <broonie@kernel.org>

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
 
@@ -289,21 +291,23 @@ 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);
 }
 
@@ -322,20 +326,14 @@ 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);
@@ -355,6 +353,59 @@ 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);