[PATCH 2/6] spi: Support multi-bus controllers

[David Lechner <dlechner@baylibre.com>]

Add support for SPI controllers with multiple physical SPI data buses.
(A data bus in this context means lines connected to a serializer, so a
controller with two data buses 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_bus
to something greater than 1. Peripherals indicate which bus they are
connected to via device tree (ACPI support can be added if needed).

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

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       | 28 +++++++++++++++++++++++++++-
 include/linux/spi/spi.h | 17 +++++++++++++++++
 2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 2e0647a06890290e1c9dc4a347a0864329795b08..84e5d5057eb41f1a522c4870265d78feb41109c8 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -2354,7 +2354,7 @@ static void of_spi_parse_dt_cs_delay(struct device_node *nc,
 static int of_spi_parse_dt(struct spi_controller *ctlr, struct spi_device *spi,
 			   struct device_node *nc)
 {
-	u32 value, cs[SPI_DEVICE_CS_CNT_MAX];
+	u32 value, buses[SPI_DEVICE_DATA_BUS_CNT_MAX], cs[SPI_DEVICE_CS_CNT_MAX];
 	int rc, idx;
 
 	/* Mode (clock phase/polarity/etc.) */
@@ -2446,6 +2446,31 @@ static int of_spi_parse_dt(struct spi_controller *ctlr, struct spi_device *spi,
 	for (idx = 0; idx < rc; idx++)
 		spi_set_chipselect(spi, idx, cs[idx]);
 
+	rc = of_property_read_variable_u32_array(nc, "spi-buses", buses, 1,
+						 ARRAY_SIZE(buses));
+	if (rc < 0 && rc != -EINVAL) {
+		dev_err(&ctlr->dev, "%pOF has invalid 'spi-buses' property (%d)\n",
+			nc, rc);
+		return rc;
+	}
+
+	if (rc == -EINVAL) {
+		/* Default when property is omitted. */
+		spi->num_data_bus = 1;
+	} else {
+		for (idx = 0; idx < rc; idx++) {
+			if (buses[idx] >= ctlr->num_data_bus) {
+				dev_err(&ctlr->dev,
+					"%pOF has out of range 'spi-buses' property (%d/%d)\n",
+					nc, buses[idx], ctlr->num_data_bus);
+				return -EINVAL;
+			}
+			spi->data_bus[idx] = buses[idx];
+		}
+
+		spi->num_data_bus = rc;
+	}
+
 	/*
 	 * By default spi->chip_select[0] will hold the physical CS number,
 	 * so set bit 0 in spi->cs_index_mask.
@@ -3054,6 +3079,7 @@ 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_bus = 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 cb2c2df3108999a73b67ef4a7b0d2cb07adfc669..c314194d4e7e2b396795ece10e142118ca05f4eb 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 buses supported per spi device */
+#define SPI_DEVICE_DATA_BUS_CNT_MAX 8
+
 struct dma_chan;
 struct software_node;
 struct ptp_system_timestamp;
@@ -171,6 +174,9 @@ extern void spi_transfer_cs_change_delay_exec(struct spi_message *msg,
  * @chip_select: Array of physical chipselect, spi->chipselect[i] gives
  *	the corresponding physical CS for logical CS i.
  * @num_chipselect: Number of physical chipselects used.
+ * @data_bus: Array of physical data buses. This is only used with specialized
+ * controllers that support multiple data buses.
+ * @num_data_bus: Number of physical data buses used.
  * @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)
@@ -231,6 +237,8 @@ struct spi_device {
 
 	u8			chip_select[SPI_DEVICE_CS_CNT_MAX];
 	u8			num_chipselect;
+	u8			data_bus[SPI_DEVICE_DATA_BUS_CNT_MAX];
+	u8			num_data_bus;
 
 	/*
 	 * Bit mask of the chipselect(s) that the driver need to use from
@@ -401,6 +409,7 @@ 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_bus: Number of data buses 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 +585,14 @@ struct spi_controller {
 	 */
 	u16			num_chipselect;
 
+	/*
+	 * Some specialized SPI controllers can have more than one physical
+	 * bus interface per controller (each having it's own serializer). This
+	 * specifies the number of buses in that case. Other controllers do not
+	 * need to set this (defaults to 1).
+	 */
+	u16			num_data_bus;
+
 	/* Some SPI controllers pose alignment requirements on DMAable
 	 * buffers; let protocol drivers know about these requirements.
 	 */

-- 
2.43.0