[U-Boot] [PATCH v2] dm: spi: prevent setting a speed of 0 Hz

[Simon Goldschmidt]

When the device tree is missing a correct spi slave description below
the bus (compatible "spi-flash" or spi-max-frequency are missing),
the 'set_speed' callback can be called with 'speed' == 0 Hz.
At least with cadence qspi, this leads to a division by zero.

Prevent this by initializing speed to 100 kHz in this case (same
fallback value as is done in 'dm_spi_claim_bus') and issue a warning
to console.

Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt at gmail.com>
---

Changes in v2:
- create a define for the 100 kHz constant (used 3 times)
- assign default value when binding new device and speed is 0
- assign default value when spi_slave_ofdata_to_platdata finds
  that spi-max-frequency property is missing

 drivers/spi/spi-uclass.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/spi/spi-uclass.c b/drivers/spi/spi-uclass.c
index b84255bd27..2bc289a74c 100644
--- a/drivers/spi/spi-uclass.c
+++ b/drivers/spi/spi-uclass.c
@@ -15,6 +15,8 @@
 
 DECLARE_GLOBAL_DATA_PTR;
 
+#define SPI_DEFAULT_SPEED_HZ 100000
+
 static int spi_set_speed_mode(struct udevice *bus, int speed, int mode)
 {
 	struct dm_spi_ops *ops;
@@ -58,7 +60,7 @@ int dm_spi_claim_bus(struct udevice *dev)
 			speed = spi->max_hz;
 	}
 	if (!speed)
-		speed = 100000;
+		speed = SPI_DEFAULT_SPEED_HZ;
 	if (speed != slave->speed) {
 		int ret = spi_set_speed_mode(bus, speed, slave->mode);
 
@@ -300,7 +302,13 @@ int spi_get_bus_and_cs(int busnum, int cs, int speed, int mode,
 		}
 		plat = dev_get_parent_platdata(dev);
 		plat->cs = cs;
-		plat->max_hz = speed;
+		if (speed) {
+			plat->max_hz = speed;
+		} else {
+			printf("Warning: SPI speed fallback to %u kHz\n",
+			       SPI_DEFAULT_SPEED_HZ / 1000);
+			plat->max_hz = SPI_DEFAULT_SPEED_HZ;
+		}
 		plat->mode = mode;
 		created = true;
 	} else if (ret) {
@@ -374,7 +382,8 @@ int spi_slave_ofdata_to_platdata(struct udevice *dev,
 	int value;
 
 	plat->cs = dev_read_u32_default(dev, "reg", -1);
-	plat->max_hz = dev_read_u32_default(dev, "spi-max-frequency", 0);
+	plat->max_hz = dev_read_u32_default(dev, "spi-max-frequency",
+					    SPI_DEFAULT_SPEED_HZ);
 	if (dev_read_bool(dev, "spi-cpol"))
 		mode |= SPI_CPOL;
 	if (dev_read_bool(dev, "spi-cpha"))
-- 
2.17.1