[PATCH v2 2/4] spi: add SPI_MOSI_IDLE_LOW mode bit

[Boerge Struempfel <boerge.struempfel@xxxxxxxxx>]

Some spi controller switch the mosi line to high, whenever they are
idle. This may not be desired in all use cases. For example neopixel
leds can get confused and flicker due to misinterpreting the idle state.
Therefore, we introduce a new spi-mode bit, with which the idle behaviour
can be overwritten on a per device basis.

Signed-off-by: Boerge Struempfel <bstruempfel@xxxxxxxxxxxxxx>
---
 drivers/spi/spi.c            | 2 ++
 include/uapi/linux/spi/spi.h | 3 ++-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 9291b2a0e8871..3ad538b317a84 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -2260,6 +2260,8 @@ static int of_spi_parse_dt(struct spi_controller *ctlr, struct spi_device *spi,
 		spi->mode |= SPI_LSB_FIRST;
 	if (of_property_read_bool(nc, "spi-cs-high"))
 		spi->mode |= SPI_CS_HIGH;
+	if (of_property_read_bool(nc, "spi-mosi-idle-low"))
+		spi->mode |= SPI_MOSI_IDLE_LOW;
 
 	/* Device DUAL/QUAD mode */
 	if (!of_property_read_u32(nc, "spi-tx-bus-width", &value)) {
diff --git a/include/uapi/linux/spi/spi.h b/include/uapi/linux/spi/spi.h
index 9d5f580597039..ca56e477d1619 100644
--- a/include/uapi/linux/spi/spi.h
+++ b/include/uapi/linux/spi/spi.h
@@ -28,6 +28,7 @@
 #define	SPI_RX_OCTAL		_BITUL(14)	/* receive with 8 wires */
 #define	SPI_3WIRE_HIZ		_BITUL(15)	/* high impedance turnaround */
 #define	SPI_RX_CPHA_FLIP	_BITUL(16)	/* flip CPHA on Rx only xfer */
+#define SPI_MOSI_IDLE_LOW	_BITUL(17)	/* leave mosi line low when idle */
 
 /*
  * All the bits defined above should be covered by SPI_MODE_USER_MASK.
@@ -37,6 +38,6 @@
  * These bits must not overlap. A static assert check should make sure of that.
  * If adding extra bits, make sure to increase the bit index below as well.
  */
-#define SPI_MODE_USER_MASK	(_BITUL(17) - 1)
+#define SPI_MODE_USER_MASK	(_BITUL(18) - 1)
 
 #endif /* _UAPI_SPI_H */
-- 
2.25.1