[PATCH v1 1/2] spi: npcm-pspi: add full duplex support

[Tomer Maimon <tmaimon77@gmail.com>]

The NPCM PSPI handler, on TX-buffer not null, would perform a dummy read
but did not save the rx-data, this was valid only for half duplex.

This patch adds full duplex support for NPCM PSPI driver by storing all
rx-data when the Rx-buffer is defined also for TX-buffer handling.

Signed-off-by: Tomer Maimon <tmaimon77@gmail.com>
---
 drivers/spi/spi-npcm-pspi.c | 75 +++++++++++++++----------------------
 1 file changed, 30 insertions(+), 45 deletions(-)

diff --git a/drivers/spi/spi-npcm-pspi.c b/drivers/spi/spi-npcm-pspi.c
index 1668a347e003..02f0fcceaf19 100644
--- a/drivers/spi/spi-npcm-pspi.c
+++ b/drivers/spi/spi-npcm-pspi.c
@@ -195,22 +195,22 @@ static void npcm_pspi_setup_transfer(struct spi_device *spi,
 static void npcm_pspi_send(struct npcm_pspi *priv)
 {
 	int wsize;
-	u16 val;
+	u16 val = 0;
 
 	wsize = min(bytes_per_word(priv->bits_per_word), priv->tx_bytes);
 	priv->tx_bytes -= wsize;
 
-	if (!priv->tx_buf)
-		return;
-
 	switch (wsize) {
 	case 1:
-		val = *priv->tx_buf++;
+		if (priv->tx_buf)
+			val = *priv->tx_buf++;
 		iowrite8(val, NPCM_PSPI_DATA + priv->base);
 		break;
 	case 2:
-		val = *priv->tx_buf++;
-		val = *priv->tx_buf++ | (val << 8);
+		if (priv->tx_buf) {
+			val = *priv->tx_buf++;
+			val = *priv->tx_buf++ | (val << 8);
+		}
 		iowrite16(val, NPCM_PSPI_DATA + priv->base);
 		break;
 	default:
@@ -222,22 +222,24 @@ static void npcm_pspi_send(struct npcm_pspi *priv)
 static void npcm_pspi_recv(struct npcm_pspi *priv)
 {
 	int rsize;
-	u16 val;
+	u16 val_16;
+	u8  val_8;
 
 	rsize = min(bytes_per_word(priv->bits_per_word), priv->rx_bytes);
 	priv->rx_bytes -= rsize;
 
-	if (!priv->rx_buf)
-		return;
-
 	switch (rsize) {
 	case 1:
-		*priv->rx_buf++ = ioread8(priv->base + NPCM_PSPI_DATA);
+		val_8 = ioread8(priv->base + NPCM_PSPI_DATA);
+		if (priv->rx_buf)
+			*priv->rx_buf++ = val_8;
 		break;
 	case 2:
-		val = ioread16(priv->base + NPCM_PSPI_DATA);
-		*priv->rx_buf++ = (val >> 8);
-		*priv->rx_buf++ = val & 0xff;
+		val_16 = ioread16(priv->base + NPCM_PSPI_DATA);
+		if (priv->rx_buf) {
+			*priv->rx_buf++ = (val_16 >> 8);
+			*priv->rx_buf++ = val_16 & 0xff;
+		}
 		break;
 	default:
 		WARN_ON_ONCE(1);
@@ -296,43 +298,26 @@ static irqreturn_t npcm_pspi_handler(int irq, void *dev_id)
 	struct npcm_pspi *priv = dev_id;
 	u8 stat;
 
-	stat = ioread8(priv->base + NPCM_PSPI_STAT);
-
 	if (!priv->tx_buf && !priv->rx_buf)
 		return IRQ_NONE;
 
-	if (priv->tx_buf) {
-		if (stat & NPCM_PSPI_STAT_RBF) {
-			ioread8(NPCM_PSPI_DATA + priv->base);
-			if (priv->tx_bytes == 0) {
-				npcm_pspi_disable(priv);
-				complete(&priv->xfer_done);
-				return IRQ_HANDLED;
-			}
-		}
-
-		if ((stat & NPCM_PSPI_STAT_BSY) == 0)
-			if (priv->tx_bytes)
-				npcm_pspi_send(priv);
+	if (priv->tx_bytes == 0 && priv->rx_bytes == 0) {
+		npcm_pspi_disable(priv);
+		complete(&priv->xfer_done);
+		return IRQ_HANDLED;
 	}
 
-	if (priv->rx_buf) {
-		if (stat & NPCM_PSPI_STAT_RBF) {
-			if (!priv->rx_bytes)
-				return IRQ_NONE;
-
-			npcm_pspi_recv(priv);
+	stat = ioread8(priv->base + NPCM_PSPI_STAT);
 
-			if (!priv->rx_bytes) {
-				npcm_pspi_disable(priv);
-				complete(&priv->xfer_done);
-				return IRQ_HANDLED;
-			}
-		}
+	/*
+	 * first we do the read since if we do the write we previous read might
+	 * be lost (indeed low chances)
+	 */
+	if ((stat & NPCM_PSPI_STAT_RBF) && priv->rx_bytes)
+		npcm_pspi_recv(priv);
 
-		if (((stat & NPCM_PSPI_STAT_BSY) == 0) && !priv->tx_buf)
-			iowrite8(0x0, NPCM_PSPI_DATA + priv->base);
-	}
+	if (((stat & NPCM_PSPI_STAT_BSY) == 0) && priv->tx_bytes)
+		npcm_pspi_send(priv);
 
 	return IRQ_HANDLED;
 }
-- 
2.33.0