spi: add more spi transfer functions

This commit adds the following spi transfer functions:
  - spi_write
  - spi_read
  - spi_write_then_read
  - spi_w8r8

The code has been ported from the linux kernel.

Signed-off-by: Hubert Feurstein <h.feurstein@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 41 insertions, 0 deletions

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 588c2633f5..64568976b2 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -195,3 +195,44 @@ int spi_sync(struct spi_device *spi, struct spi_message *message)
 	return spi->master->transfer(spi, message);
 }
 
+/**
+ * spi_write_then_read - SPI synchronous write followed by read
+ * @spi: device with which data will be exchanged
+ * @txbuf: data to be written
+ * @n_tx: size of txbuf, in bytes
+ * @rxbuf: buffer into which data will be read
+ * @n_rx: size of rxbuf, in bytes
+ * Context: can sleep
+ *
+ * This performs a half duplex MicroWire style transaction with the
+ * device, sending txbuf and then reading rxbuf.  The return value
+ * is zero for success, else a negative errno status code.
+ * This call may only be used from a context that may sleep.
+ */
+int spi_write_then_read(struct spi_device *spi,
+		const void *txbuf, unsigned n_tx,
+		void *rxbuf, unsigned n_rx)
+{
+	int			status;
+	struct spi_message	message;
+	struct spi_transfer	x[2];
+
+	spi_message_init(&message);
+	memset(x, 0, sizeof x);
+	if (n_tx) {
+		x[0].len = n_tx;
+		spi_message_add_tail(&x[0], &message);
+	}
+	if (n_rx) {
+		x[1].len = n_rx;
+		spi_message_add_tail(&x[1], &message);
+	}
+
+	x[0].tx_buf = txbuf;
+	x[1].rx_buf = rxbuf;
+
+	/* do the i/o */
+	status = spi_sync(spi, &message);
+	return status;
+}
+EXPORT_SYMBOL(spi_write_then_read);