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Subject[PATCH v4 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 v3 -> v4:
* https://lore.kernel.org/linux-spi/20201127130834.136348-2-alexandru.ardelean@analog.com/
* moved SPI_NO_TX + SPI_NO_RX to internal spi.h header
* added SPI_MODE_USER_MASK & SPI_MODE_KERNEL_MASK + BUILD_BUG_ON() check

drivers/spi/spi.c | 28 +++++++++++++++++++++++-----
include/linux/spi/spi.h | 4 ++++
include/uapi/linux/spi/spi.h | 6 ++++++
3 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index cd3c395b4e90..8668626c4a46 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1941,6 +1941,9 @@ 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:
@@ -1962,6 +1965,9 @@ 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:
@@ -3329,12 +3335,17 @@ 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
@@ -3348,7 +3359,8 @@ 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.
*/
@@ -3609,6 +3621,8 @@ 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)
@@ -3622,6 +3636,8 @@ 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)
@@ -4190,6 +4206,8 @@ static int __init spi_init(void)
{
int status;

+ BUILD_BUG_ON(SPI_MODE_USER_MASK & SPI_MODE_KERNEL_MASK);
+
buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL);
if (!buf) {
status = -ENOMEM;
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index a08c3f37e202..6f1905f729c4 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -6,6 +6,7 @@
#ifndef __LINUX_SPI_H
#define __LINUX_SPI_H

+#include <linux/bits.h>
#include <linux/device.h>
#include <linux/mod_devicetable.h>
#include <linux/slab.h>
@@ -166,6 +167,9 @@ struct spi_device {
u8 chip_select;
u8 bits_per_word;
bool rt;
+#define SPI_NO_TX BIT(31) /* no transmit wire */
+#define SPI_NO_RX BIT(30) /* no receive wire */
+#define SPI_MODE_KERNEL_MASK (SPI_NO_TX | SPI_NO_RX)
u32 mode;
int irq;
void *controller_state;
diff --git a/include/uapi/linux/spi/spi.h b/include/uapi/linux/spi/spi.h
index 703b586f35df..e5c58748422e 100644
--- a/include/uapi/linux/spi/spi.h
+++ b/include/uapi/linux/spi/spi.h
@@ -28,4 +28,10 @@
#define SPI_RX_OCTAL _BITUL(14) /* receive with 8 wires */
#define SPI_3WIRE_HIZ _BITUL(15) /* high impedance turnaround */

+#define SPI_MODE_USER_MASK \
+ (SPI_CPHA | SPI_CPOL | SPI_CS_HIGH | SPI_LSB_FIRST | \
+ SPI_3WIRE | SPI_LOOP | SPI_NO_CS | SPI_READY | \
+ SPI_TX_DUAL | SPI_TX_QUAD | SPI_RX_DUAL | SPI_RX_QUAD | \
+ SPI_CS_WORD | SPI_TX_OCTAL | SPI_RX_OCTAL | SPI_3WIRE_HIZ)
+
#endif /* _UAPI_SPI_H */
--
2.17.1
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