[PATCH v5 3/9] spi: support controllers with multiple data lanes

David Lechner
2026-01-12T17:46:32Z

Add support for SPI controllers with multiple physical SPI data lanes.
(A data lane in this context means lines connected to a serializer, so a
controller with two data lanes would have two serializers in a single
controller).

This is common in the type of controller that can be used with parallel
flash memories, but can be used for general purpose SPI as well.

To indicate support, a controller just needs to set ctlr->num_data_lanes
to something greater than 1. Peripherals indicate which lane they are
connected to via device tree (ACPI support can be added if needed).

The spi-{tx,rx}-bus-width DT properties can now be arrays. The length of
the array indicates the number of data lanes, and each element indicates
the bus width of that lane. For now, we restrict all lanes to have the
same bus width to keep things simple. Support for an optional controller
lane mapping property is also implemented.

Signed-off-by: David Lechner <dlechner@baylibre.com>
---

v5 changes:
- Use of_property_read_variable_u32_array() for lane maps.

v4 changes:
- Update for changes in devicetree bindings.
- Don't put new fields in the middle of CS fields.
- Dropped acks since this was a significant rework.

v3 changes:
* Renamed "buses" to "lanes" to reflect devicetree property name change.

This patch has been seen in a different series [1] by Sean before:

[1]: https://lore.kernel.org/linux-spi/20250616220054.3968946-4-sean.anderson@linux.dev/

Changes:
* Use u8 array instead of bitfield so that the order of the mapping is
preserved. (Now looks very much like chip select mapping.)
* Added doc strings for added fields.
* Tweaked the comments.
---
drivers/spi/spi.c | 116 +++++++++++++++++++++++++++++++++++++++++++++++-
include/linux/spi/spi.h | 22 +++++++++
2 files changed, 136 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index e25df9990f82..5c3f9ba3f606 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -2370,7 +2370,53 @@ static int of_spi_parse_dt(struct spi_controller *ctlr, struct spi_device *spi,
spi->mode |= SPI_CS_HIGH;

/* Device DUAL/QUAD mode */
- if (!of_property_read_u32(nc, "spi-tx-bus-width", &value)) {
+
+ rc = of_property_read_variable_u32_array(nc, "spi-tx-lane-map",
+ spi->tx_lane_map, 1,
+ ARRAY_SIZE(spi->tx_lane_map));
+ if (rc == -EINVAL) {
+ /* Default lane map */
+ for (idx = 0; idx < ARRAY_SIZE(spi->tx_lane_map); idx++)
+ spi->tx_lane_map[idx] = idx;
+ } else if (rc < 0) {
+ dev_err(&ctlr->dev,
+ "failed to read spi-tx-lane-map property: %d\n", rc);
+ return rc;
+ }
+
+ rc = of_property_count_u32_elems(nc, "spi-tx-bus-width");
+ if (rc < 0 && rc != -EINVAL) {
+ dev_err(&ctlr->dev,
+ "failed to read spi-tx-bus-width property: %d\n", rc);
+ return rc;
+ }
+
+ if (rc == -EINVAL) {
+ /* Default when property is not present. */
+ spi->num_tx_lanes = 1;
+ } else {
+ u32 first_value;
+
+ spi->num_tx_lanes = rc;
+
+ for (idx = 0; idx < spi->num_tx_lanes; idx++) {
+ of_property_read_u32_index(nc, "spi-tx-bus-width", idx,
+ &value);
+
+ /*
+ * For now, we only support all lanes having the same
+ * width so we can keep using the existing mode flags.
+ */
+ if (!idx)
+ first_value = value;
+ else if (first_value != value) {
+ dev_err(&ctlr->dev,
+ "spi-tx-bus-width has inconsistent values: first %d vs later %d\n",
+ first_value, value);
+ return -EINVAL;
+ }
+ }
+
switch (value) {
case 0:
spi->mode |= SPI_NO_TX;
@@ -2394,7 +2440,62 @@ 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)) {
+ for (idx = 0; idx < spi->num_tx_lanes; idx++) {
+ if (spi->tx_lane_map[idx] >= spi->controller->num_data_lanes) {
+ dev_err(&ctlr->dev,
+ "spi-tx-lane-map has invalid value %d (num_data_lanes=%d)\n",
+ spi->tx_lane_map[idx],
+ spi->controller->num_data_lanes);
+ return -EINVAL;
+ }
+ }
+
+ rc = of_property_read_variable_u32_array(nc, "spi-rx-lane-map",
+ spi->rx_lane_map, 1,
+ ARRAY_SIZE(spi->rx_lane_map));
+ if (rc == -EINVAL) {
+ /* Default lane map */
+ for (idx = 0; idx < ARRAY_SIZE(spi->rx_lane_map); idx++)
+ spi->rx_lane_map[idx] = idx;
+ } else if (rc < 0) {
+ dev_err(&ctlr->dev,
+ "failed to read spi-rx-lane-map property: %d\n", rc);
+ return rc;
+ }
+
+ rc = of_property_count_u32_elems(nc, "spi-rx-bus-width");
+ if (rc < 0 && rc != -EINVAL) {
+ dev_err(&ctlr->dev,
+ "failed to read spi-rx-bus-width property: %d\n", rc);
+ return rc;
+ }
+
+ if (rc == -EINVAL) {
+ /* Default when property is not present. */
+ spi->num_rx_lanes = 1;
+ } else {
+ u32 first_value;
+
+ spi->num_rx_lanes = rc;
+
+ for (idx = 0; idx < spi->num_rx_lanes; idx++) {
+ of_property_read_u32_index(nc, "spi-rx-bus-width", idx,
+ &value);
+
+ /*
+ * For now, we only support all lanes having the same
+ * width so we can keep using the existing mode flags.
+ */
+ if (!idx)
+ first_value = value;
+ else if (first_value != value) {
+ dev_err(&ctlr->dev,
+ "spi-rx-bus-width has inconsistent values: first %d vs later %d\n",
+ first_value, value);
+ return -EINVAL;
+ }
+ }
+
switch (value) {
case 0:
spi->mode |= SPI_NO_RX;
@@ -2418,6 +2519,16 @@ static int of_spi_parse_dt(struct spi_controller *ctlr, struct spi_device *spi,
}
}

+ for (idx = 0; idx < spi->num_rx_lanes; idx++) {
+ if (spi->rx_lane_map[idx] >= spi->controller->num_data_lanes) {
+ dev_err(&ctlr->dev,
+ "spi-rx-lane-map has invalid value %d (num_data_lanes=%d)\n",
+ spi->rx_lane_map[idx],
+ spi->controller->num_data_lanes);
+ return -EINVAL;
+ }
+ }
+
if (spi_controller_is_target(ctlr)) {
if (!of_node_name_eq(nc, "slave")) {
dev_err(&ctlr->dev, "%pOF is not called 'slave'\n",
@@ -3066,6 +3177,7 @@ struct spi_controller *__spi_alloc_controller(struct device *dev,
mutex_init(&ctlr->add_lock);
ctlr->bus_num = -1;
ctlr->num_chipselect = 1;
+ ctlr->num_data_lanes = 1;
ctlr->target = target;
if (IS_ENABLED(CONFIG_SPI_SLAVE) && target)
ctlr->dev.class = &spi_target_class;
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index cb2c2df31089..7aff60ab257e 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -23,6 +23,9 @@
/* Max no. of CS supported per spi device */
#define SPI_DEVICE_CS_CNT_MAX 4

+/* Max no. of data lanes supported per spi device */
+#define SPI_DEVICE_DATA_LANE_CNT_MAX 8
+
struct dma_chan;
struct software_node;
struct ptp_system_timestamp;
@@ -174,6 +177,10 @@ extern void spi_transfer_cs_change_delay_exec(struct spi_message *msg,
* @cs_index_mask: Bit mask of the active chipselect(s) in the chipselect array
* @cs_gpiod: Array of GPIO descriptors of the corresponding chipselect lines
* (optional, NULL when not using a GPIO line)
+ * @tx_lane_map: Map of peripheral lanes (index) to controller lanes (value).
+ * @num_tx_lanes: Number of transmit lanes wired up.
+ * @rx_lane_map: Map of peripheral lanes (index) to controller lanes (value).
+ * @num_rx_lanes: Number of receive lanes wired up.
*
* A @spi_device is used to interchange data between an SPI target device
* (usually a discrete chip) and CPU memory.
@@ -242,6 +249,12 @@ struct spi_device {

struct gpio_desc *cs_gpiod[SPI_DEVICE_CS_CNT_MAX]; /* Chip select gpio desc */

+ /* Multi-lane SPI controller support. */
+ u32 tx_lane_map[SPI_DEVICE_DATA_LANE_CNT_MAX];
+ u32 num_tx_lanes;
+ u32 rx_lane_map[SPI_DEVICE_DATA_LANE_CNT_MAX];
+ u32 num_rx_lanes;
+
/*
* Likely need more hooks for more protocol options affecting how
* the controller talks to each chip, like:
@@ -401,6 +414,7 @@ extern struct spi_device *spi_new_ancillary_device(struct spi_device *spi, u8 ch
* SPI targets, and are numbered from zero to num_chipselects.
* each target has a chipselect signal, but it's common that not
* every chipselect is connected to a target.
+ * @num_data_lanes: Number of data lanes supported by this controller. Default is 1.
* @dma_alignment: SPI controller constraint on DMA buffers alignment.
* @mode_bits: flags understood by this controller driver
* @buswidth_override_bits: flags to override for this controller driver
@@ -576,6 +590,14 @@ struct spi_controller {
*/
u16 num_chipselect;

+ /*
+ * Some specialized SPI controllers can have more than one physical
+ * data lane interface per controller (each having it's own serializer).
+ * This specifies the number of data lanes in that case. Other
+ * controllers do not need to set this (defaults to 1).
+ */
+ u16 num_data_lanes;
+
/* Some SPI controllers pose alignment requirements on DMAable
* buffers; let protocol drivers know about these requirements.
*/

--
2.43.0