spi: a3700: Allow to enable or disable FIFO mode

The armada 3700 SPI controller allows to make transfers without using
the 32 bytes RFIFO and WFIFO.

This commit enable switching between FIFO and non-FIFO mode, which is
necessary to implement full-duplex transfers.
Signed-off-by: Maxime Chevallier <maxime.chevallier@smile.fr>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-armada-3700.c

@@ -185,12 +185,15 @@ static int a3700_spi_pin_mode_set(struct a3700_spi *a3700_spi,
 	return 0;
 }
 
-static void a3700_spi_fifo_mode_set(struct a3700_spi *a3700_spi)
+static void a3700_spi_fifo_mode_set(struct a3700_spi *a3700_spi, bool enable)
 {
 	u32 val;
 
 	val = spireg_read(a3700_spi, A3700_SPI_IF_CFG_REG);
-	val |= A3700_SPI_FIFO_MODE;
+	if (enable)
+		val |= A3700_SPI_FIFO_MODE;
+	else
+		val &= ~A3700_SPI_FIFO_MODE;
 	spireg_write(a3700_spi, A3700_SPI_IF_CFG_REG, val);
 }
 
@@ -291,7 +294,7 @@ static int a3700_spi_init(struct a3700_spi *a3700_spi)
 		a3700_spi_deactivate_cs(a3700_spi, i);
 
 	/* Enable FIFO mode */
-	a3700_spi_fifo_mode_set(a3700_spi);
+	a3700_spi_fifo_mode_set(a3700_spi, true);
 
 	/* Set SPI mode */
 	a3700_spi_mode_set(a3700_spi, master->mode_bits);