From: Dragos Bogdan <dragos.bog...@analog.com>

Transmit/receive only is a valid SPI mode. For example, the MOSI/TX line
might be missing from an ADC while for a DAC the MISO/RX line may be
optional. This patch adds these two new modes: SPI_NO_TX and
SPI_NO_RX. This way, the drivers will be able to identify if any of
these two lines is missing and to adjust the transfers accordingly.

Signed-off-by: Dragos Bogdan <dragos.bog...@analog.com>
Signed-off-by: Alexandru Ardelean <alexandru.ardel...@analog.com>
---

Changelog v1 -> v2:
* 
https://lore.kernel.org/linux-spi/20201111141529.98147-1-alexandru.ardel...@analog.com/
* convert comment to new multi-line format

 drivers/spi/spi.c       | 26 +++++++++++++++++++++-----
 include/linux/spi/spi.h |  2 ++
 2 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 0c3f3a962448..5784fa8d9d74 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1939,6 +1939,9 @@ static int of_spi_parse_dt(struct spi_controller *ctlr, 
struct spi_device *spi,
        /* Device DUAL/QUAD mode */
        if (!of_property_read_u32(nc, "spi-tx-bus-width", &value)) {
                switch (value) {
+               case 0:
+                       spi->mode |= SPI_NO_TX;
+                       break;
                case 1:
                        break;
                case 2:
@@ -1960,6 +1963,9 @@ static int of_spi_parse_dt(struct spi_controller *ctlr, 
struct spi_device *spi,
 
        if (!of_property_read_u32(nc, "spi-rx-bus-width", &value)) {
                switch (value) {
+               case 0:
+                       spi->mode |= SPI_NO_RX;
+                       break;
                case 1:
                        break;
                case 2:
@@ -3327,12 +3333,17 @@ int spi_setup(struct spi_device *spi)
        unsigned        bad_bits, ugly_bits;
        int             status;
 
-       /* check mode to prevent that DUAL and QUAD set at the same time
+       /*
+        * check mode to prevent that any two of DUAL, QUAD and NO_MOSI/MISO
+        * are set at the same time
         */
-       if (((spi->mode & SPI_TX_DUAL) && (spi->mode & SPI_TX_QUAD)) ||
-               ((spi->mode & SPI_RX_DUAL) && (spi->mode & SPI_RX_QUAD))) {
+       if ((hweight_long(spi->mode &
+               (SPI_TX_DUAL | SPI_TX_QUAD | SPI_NO_TX)) > 1) ||
+           (hweight_long(spi->mode &
+               (SPI_RX_DUAL | SPI_RX_QUAD | SPI_NO_RX)) > 1)) {
                dev_err(&spi->dev,
-               "setup: can not select dual and quad at the same time\n");
+               "setup: can not select any two of dual, quad and no-rx/tx "
+               "at the same time\n");
                return -EINVAL;
        }
        /* if it is SPI_3WIRE mode, DUAL and QUAD should be forbidden
@@ -3346,7 +3357,8 @@ int spi_setup(struct spi_device *spi)
         * SPI_CS_WORD has a fallback software implementation,
         * so it is ignored here.
         */
-       bad_bits = spi->mode & ~(spi->controller->mode_bits | SPI_CS_WORD);
+       bad_bits = spi->mode & ~(spi->controller->mode_bits | SPI_CS_WORD |
+                                SPI_NO_TX | SPI_NO_RX);
        /* nothing prevents from working with active-high CS in case if it
         * is driven by GPIO.
         */
@@ -3607,6 +3619,8 @@ static int __spi_validate(struct spi_device *spi, struct 
spi_message *message)
                 * 2. check tx/rx_nbits match the mode in spi_device
                 */
                if (xfer->tx_buf) {
+                       if (spi->mode & SPI_NO_TX)
+                               return -EINVAL;
                        if (xfer->tx_nbits != SPI_NBITS_SINGLE &&
                                xfer->tx_nbits != SPI_NBITS_DUAL &&
                                xfer->tx_nbits != SPI_NBITS_QUAD)
@@ -3620,6 +3634,8 @@ static int __spi_validate(struct spi_device *spi, struct 
spi_message *message)
                }
                /* check transfer rx_nbits */
                if (xfer->rx_buf) {
+                       if (spi->mode & SPI_NO_RX)
+                               return -EINVAL;
                        if (xfer->rx_nbits != SPI_NBITS_SINGLE &&
                                xfer->rx_nbits != SPI_NBITS_DUAL &&
                                xfer->rx_nbits != SPI_NBITS_QUAD)
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 66c7d8e45563..8f3343d3ac27 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -186,6 +186,8 @@ struct spi_device {
 #define        SPI_TX_OCTAL    BIT(13)                 /* transmit with 8 
wires */
 #define        SPI_RX_OCTAL    BIT(14)                 /* receive with 8 wires 
*/
 #define        SPI_3WIRE_HIZ   BIT(15)                 /* high impedance 
turnaround */
+#define        SPI_NO_TX       BIT(16)                 /* no transmit wire */
+#define        SPI_NO_RX       BIT(17)                 /* no receive wire */
        int                     irq;
        void                    *controller_state;
        void                    *controller_data;
-- 
2.17.1

Reply via email to