[PATCH 2/2] spi: add support for all spi modes with soft spi

[Johannes Holland]

The spi bitbanging driver did not implement all spi modes properly. Add
code to support all spi modes, honoring soft_spi_set_mode() and
defaulting to spi mode 0. Previously, CPHA was implemented inversely
(defaulting to CPHA=1) and CPOL=1 was hardcoded.

Signed-off-by: Johannes Holland <johannes.holland at infineon.com>
---
 drivers/spi/soft_spi.c | 48 ++++++++++++++++++++++++++++++++----------
 1 file changed, 37 insertions(+), 11 deletions(-)

diff --git a/drivers/spi/soft_spi.c b/drivers/spi/soft_spi.c
index b80f810bd1..08b6c53315 100644
--- a/drivers/spi/soft_spi.c
+++ b/drivers/spi/soft_spi.c
@@ -58,10 +58,12 @@ static int soft_spi_sda(struct udevice *dev, int bit)
 static int soft_spi_cs_activate(struct udevice *dev)
 {
 	struct udevice *bus = dev_get_parent(dev);
+	struct soft_spi_priv *priv = dev_get_priv(bus);
 	struct soft_spi_platdata *plat = dev_get_platdata(bus);
+	int cidle = !!(priv->mode & SPI_CPOL);
 
 	dm_gpio_set_value(&plat->cs, 0);
-	dm_gpio_set_value(&plat->sclk, 0);
+	dm_gpio_set_value(&plat->sclk, cidle); /* to idle */
 	dm_gpio_set_value(&plat->cs, 1);
 
 	return 0;
@@ -79,11 +81,14 @@ static int soft_spi_cs_deactivate(struct udevice *dev)
 
 static int soft_spi_claim_bus(struct udevice *dev)
 {
+	struct udevice *bus = dev_get_parent(dev);
+	struct soft_spi_priv *priv = dev_get_priv(bus);
+	int cidle = !!(priv->mode & SPI_CPOL);
 	/*
 	 * Make sure the SPI clock is in idle state as defined for
 	 * this slave.
 	 */
-	return soft_spi_scl(dev, 0);
+	return soft_spi_scl(dev, cidle);
 }
 
 static int soft_spi_release_bus(struct udevice *dev)
@@ -114,7 +119,8 @@ static int soft_spi_xfer(struct udevice *dev, unsigned int bitlen,
 	uchar		tmpdout = 0;
 	const u8	*txd = dout;
 	u8		*rxd = din;
-	int		cpha = priv->mode & SPI_CPHA;
+	int		cpha = !!(priv->mode & SPI_CPHA);
+	int		cidle = !!(priv->mode & SPI_CPOL);
 	unsigned int	j;
 
 	debug("spi_xfer: slave %s:%s dout %08X din %08X bitlen %u\n",
@@ -140,22 +146,42 @@ static int soft_spi_xfer(struct udevice *dev, unsigned int bitlen,
 			tmpdin  = 0;
 		}
 
-		if (!cpha)
-			soft_spi_scl(dev, 0);
+		/*
+		 * CPOL 0: idle is low (0), active is high (1)
+		 * CPOL 1: idle is high (1), active is low (0)
+		 */
+
+		/*
+		 * drive bit
+		 *  CPHA 1: CLK from idle to active
+		 */
+		if (cpha)
+			soft_spi_scl(dev, !cidle);
 		if ((plat->flags & SPI_MASTER_NO_TX) == 0)
 			soft_spi_sda(dev, !!(tmpdout & 0x80));
 		udelay(plat->spi_delay_us);
-		if (cpha)
-			soft_spi_scl(dev, 0);
+
+		/*
+		 * sample bit
+		 *  CPHA 0: CLK from idle to active
+		 *  CPHA 1: CLK from active to idle
+		 */
+		if (!cpha)
+			soft_spi_scl(dev, !cidle);
 		else
-			soft_spi_scl(dev, 1);
+			soft_spi_scl(dev, cidle);
 		tmpdin	<<= 1;
 		if ((plat->flags & SPI_MASTER_NO_RX) == 0)
 			tmpdin	|= dm_gpio_get_value(&plat->miso);
 		tmpdout	<<= 1;
 		udelay(plat->spi_delay_us);
-		if (cpha)
-			soft_spi_scl(dev, 1);
+
+		/*
+		 * drive bit
+		 *  CPHA 0: CLK from active to idle
+		 */
+		if (!cpha)
+			soft_spi_scl(dev, cidle);
 	}
 	/*
 	 * If the number of bits isn't a multiple of 8, shift the last
@@ -176,7 +202,7 @@ static int soft_spi_xfer(struct udevice *dev, unsigned int bitlen,
 
 static int soft_spi_set_speed(struct udevice *dev, unsigned int speed)
 {
-	/* Accept any speed */
+	/* Ignore any speed settings. Speed is implemented via "spi-delay-us" */
 	return 0;
 }
 
-- 
2.26.1