[PATCH v2 4/9] spi: Add flag to determine default bus

[Sean Anderson <sean.anderson@linux.dev>]

The ZynqMP GQSPI driver determines the default SPI bus based on the chip
select. For compatibility, introduce a flag to determine the buses from
the chipselect when the spi-buses property is absent.

Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
---

Changes in v2:
- New

 drivers/spi/spi.c       | 7 ++++++-
 include/linux/spi/spi.h | 2 ++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 9fbf069623a8..d9d0c24cee0b 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -2470,7 +2470,12 @@ static int of_spi_parse_dt(struct spi_controller *ctlr, struct spi_device *spi,
 
 	if (rc == -EINVAL) {
 		/* Default when property is omitted. */
-		spi->buses = BIT(0);
+		if ((ctlr->flags & SPI_CONTROLLER_DEFAULT_BUS_IS_CS) &&
+		    cs[0] != SPI_INVALID_CS && cs[0] < ctlr->num_buses) {
+			spi->buses = BIT(cs[0]);
+		} else {
+			spi->buses = BIT(0);
+		}
 	} else {
 		for (idx = 0; idx < rc; idx++) {
 			if (buses[idx] >= ctlr->num_buses) {
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 70e8e6555a33..cea93b0895b9 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -621,6 +621,8 @@ struct spi_controller {
 	 * assert/de-assert more than one chip select at once.
 	 */
 #define SPI_CONTROLLER_MULTI_CS		BIT(7)
+	/* spi_device->buses defaults to spi_device->cs[0] */
+#define SPI_CONTROLLER_DEFAULT_BUS_IS_CS BIT(8)
 
 	/* Flag indicating if the allocation of this struct is devres-managed */
 	bool			devm_allocated;
-- 
2.35.1.1320.gc452695387.dirty