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Subject[PATCH v2 2/3] spi: Add SPI_NO_TX/RX support
Date
From: Dragos Bogdan <dragos.bogdan@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.bogdan@analog.com>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
---

Changelog v1 -> v2:
* https://lore.kernel.org/linux-spi/20201111141529.98147-1-alexandru.ardelean@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
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