[PATCH v6 2/3] spi: Add SPI_NO_TX/RX support

From: Alexandru Ardelean
Date: Mon Dec 21 2020 - 10:26:17 EST

From: Dragos Bogdan <dragos.bogdan@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
---

Changelog v5 -> v6:
* https://patchwork.kernel.org/project/spi-devel-general/patch/20201221141906.48922-2-alexandru.ardelean@xxxxxxxxxx/
* merged on single line message:
"setup: can not select any two of dual, quad and no-rx/tx at the same time\n"
* not adding Reviewed-by: tag for Andy yet, since there was a nit

drivers/spi/spi.c | 25 ++++++++++++++++++++-----
include/linux/spi/spi.h | 17 +++++++++++++++++
include/uapi/linux/spi/spi.h | 10 ++++++++++
3 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 51d7c004fbab..ca75f4036eda 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 +3335,16 @@ 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 +3358,8 @@ 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.
*/
@@ -3610,6 +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)
@@ -3623,6 +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)
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index a08c3f37e202..9bfdfaf286eb 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 +167,18 @@ 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 */
+ /*
+ * All bits defined above should be covered by SPI_MODE_KERNEL_MASK.
+ * The SPI_MODE_KERNEL_MASK has the SPI_MODE_USER_MASK counterpart,
+ * which is defined in 'include/uapi/linux/spi/spi.h'.
+ * The bits defined here are from bit 31 downwards, while in
+ * SPI_MODE_USER_MASK are from 0 upwards.
+ * These bits must not overlap. A static assert check should make sure of that.
+ * If adding extra bits, make sure to decrease the bit index below as well.
+ */
+#define SPI_MODE_KERNEL_MASK (~(BIT(30) - 1))
u32 mode;
int irq;
void *controller_state;
@@ -189,6 +202,10 @@ struct spi_device {
*/
};

+/* Make sure that SPI_MODE_KERNEL_MASK & SPI_MODE_USER_MASK don't overlap */
+static_assert((SPI_MODE_KERNEL_MASK & SPI_MODE_USER_MASK) == 0,
+ "SPI_MODE_USER_MASK & SPI_MODE_KERNEL_MASK must not overlap");
+
static inline struct spi_device *to_spi_device(struct device *dev)
{
return dev ? container_of(dev, struct spi_device, dev) : NULL;
diff --git a/include/uapi/linux/spi/spi.h b/include/uapi/linux/spi/spi.h
index 703b586f35df..236a85f08ded 100644
--- a/include/uapi/linux/spi/spi.h
+++ b/include/uapi/linux/spi/spi.h
@@ -28,4 +28,14 @@
#define SPI_RX_OCTAL _BITUL(14) /* receive with 8 wires */
#define SPI_3WIRE_HIZ _BITUL(15) /* high impedance turnaround */

+/*
+ * All the bits defined above should be covered by SPI_MODE_USER_MASK.
+ * The SPI_MODE_USER_MASK has the SPI_MODE_KERNEL_MASK counterpart in
+ * 'include/linux/spi/spi.h'. The bits defined here are from bit 0 upwards
+ * while in SPI_MODE_KERNEL_MASK they are from the other end downwards.
+ * 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(16) - 1)
+
#endif /* _UAPI_SPI_H */
--
2.17.1