[U-Boot] [PATCH 1/4] spi: spi-mem: Add optional half-duplex SPI transfer mode

[Stefan Roese <sr@denx.de>]

Some SPI controller might now support full-duplex SPI transfers.
This option can be enabled to use half-duplex operation mode for
such SPI controllers.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Boris Brezillon <boris.brezillon@bootlin.com>
Cc: Jagan Teki <jagan@openedev.com>
---
 drivers/spi/Kconfig   |  8 ++++++++
 drivers/spi/spi-mem.c | 31 ++++++++++++++++++++++++++++---
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index 9fbd26740d..5bd8289284 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -25,6 +25,14 @@ config SPI_MEM
 	  This extension is meant to simplify interaction with SPI memories
 	  by providing an high-level interface to send memory-like commands.
 
+config SPI_MEM_HALF_DUPLEX
+	bool "Use half-duplex SPI transfer"
+	depends on SPI_MEM
+	help
+	  Some SPI controller might not support full-duplex SPI transfers.
+	  This option can be enabled to use half-duplex operation mode for
+	  such SPI controllers.
+
 config ALTERA_SPI
 	bool "Altera SPI driver"
 	help
diff --git a/drivers/spi/spi-mem.c b/drivers/spi/spi-mem.c
index 07ce799170..617fbbfe09 100644
--- a/drivers/spi/spi-mem.c
+++ b/drivers/spi/spi-mem.c
@@ -202,6 +202,10 @@ int spi_mem_exec_op(struct spi_slave *slave, const struct spi_mem_op *op)
 	struct dm_spi_ops *ops = spi_get_ops(bus);
 	unsigned int xfer_len, pos = 0;
 	u8 *tx_buf, *rx_buf = NULL;
+	unsigned int pos2;
+	int tx_len;
+	int rx_len;
+	u32 flag;
 	int ret;
 	int i;
 
@@ -370,8 +374,29 @@ int spi_mem_exec_op(struct spi_slave *slave, const struct spi_mem_op *op)
 	if (tx_data)
 		memcpy(tx_buf + pos, op->data.buf.out, op->data.nbytes);
 
-	ret = spi_xfer(slave, xfer_len * 8, tx_buf, rx_buf,
-		       SPI_XFER_BEGIN | SPI_XFER_END);
+	pos2 = pos;
+	if (CONFIG_IS_ENABLED(SPI_MEM_HALF_DUPLEX)) {
+		if (rx_data) {
+			tx_len = (sizeof(op->cmd.opcode) +
+				  op->addr.nbytes + op->dummy.nbytes);
+			rx_len = op->data.nbytes;
+			flag = SPI_XFER_BEGIN;
+			pos2 = 0;
+		} else {
+			tx_len = xfer_len;
+			rx_len = 0;
+			flag = SPI_XFER_BEGIN | SPI_XFER_END;
+		}
+		ret = spi_xfer(slave, tx_len * 8, tx_buf, NULL, flag);
+		if (rx_data) {
+			ret = spi_xfer(slave, rx_len * 8, NULL,
+				       rx_buf, SPI_XFER_END);
+		}
+	} else {
+		ret = spi_xfer(slave, xfer_len * 8, tx_buf, rx_buf,
+			       SPI_XFER_BEGIN | SPI_XFER_END);
+	}
+
 	spi_release_bus(slave);
 
 	for (i = 0; i < pos; i++)
@@ -387,7 +412,7 @@ int spi_mem_exec_op(struct spi_slave *slave, const struct spi_mem_op *op)
 		return ret;
 
 	if (rx_data)
-		memcpy(op->data.buf.in, rx_buf + pos, op->data.nbytes);
+		memcpy(op->data.buf.in, rx_buf + pos2, op->data.nbytes);
 
 	kfree(tx_buf);
 	kfree(rx_buf);
-- 
2.18.0