[PATCH v3 1/6] spi: Add SPI mode bit for MOSI idle state configuration

[Marcelo Schmitt]

The behavior of an SPI controller data output line (SDO or MOSI or COPI
(Controller Output Peripheral Input) for disambiguation) is not specified
when the controller is not clocking out data on SCLK edges. However, there
exist SPI peripherals that require specific COPI line state when data is
not being clocked out of the controller.
Add SPI mode bit to allow pheripherals to request explicit COPI idle
behavior when needed.

Signed-off-by: Marcelo Schmitt <marcelo.schmitt@xxxxxxxxxx>
---
 drivers/spi/spi.c            | 6 ++++++
 include/uapi/linux/spi/spi.h | 3 ++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 289feccca376..6072b6e93bef 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -3921,6 +3921,12 @@ int spi_setup(struct spi_device *spi)
 		(SPI_TX_DUAL | SPI_TX_QUAD | SPI_TX_OCTAL |
 		 SPI_RX_DUAL | SPI_RX_QUAD | SPI_RX_OCTAL)))
 		return -EINVAL;
+	/* Check against conflicting MOSI idle configuration */
+	if ((spi->mode & SPI_MOSI_IDLE_LOW) && (spi->mode & SPI_MOSI_IDLE_HIGH)) {
+		dev_warn(&spi->dev,
+			 "setup: erratic MOSI idle configuration. Set to idle low\n");
+		spi->mode &= ~SPI_MOSI_IDLE_HIGH;
+	}
 	/*
 	 * Help drivers fail *cleanly* when they need options
 	 * that aren't supported with their current controller.
diff --git a/include/uapi/linux/spi/spi.h b/include/uapi/linux/spi/spi.h
index ca56e477d161..ba9adba25927 100644
--- a/include/uapi/linux/spi/spi.h
+++ b/include/uapi/linux/spi/spi.h
@@ -29,6 +29,7 @@
 #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 */
+#define SPI_MOSI_IDLE_HIGH	_BITUL(18)	/* leave mosi line high when idle */
 
 /*
  * All the bits defined above should be covered by SPI_MODE_USER_MASK.
@@ -38,6 +39,6 @@
  * 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(18) - 1)
+#define SPI_MODE_USER_MASK	(_BITUL(19) - 1)
 
 #endif /* _UAPI_SPI_H */
-- 
2.43.0