dm: spi: Avoid setting the speed with every transfer

Only set the speed if it has changed from last time. Since the speed will
be 0 when the device is probed it will always be changed on the first
transfer after the device is probed.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/spi/spi-uclass.c

@@ -63,9 +63,12 @@ int spi_claim_bus(struct spi_slave *slave)
 	}
 	if (!speed)
 		speed = 100000;
+	if (speed != slave->speed) {
 		ret = spi_set_speed_mode(bus, speed, slave->mode);
 		if (ret)
 			return ret;
+		slave->speed = speed;
+	}
 
 	return ops->claim_bus ? ops->claim_bus(dev) : 0;
 }

include/spi.h

@@ -100,6 +100,8 @@ struct dm_spi_slave_platdata {
  * @dev:		SPI slave device
  * @max_hz:		Maximum speed for this slave
  * @mode:		SPI mode to use for this slave (see SPI mode flags)
+ * @speed:		Current bus speed. This is 0 until the bus is first
+ *			claimed.
  * @bus:		ID of the bus that the slave is attached to. For
  *			driver model this is the sequence number of the SPI
  *			bus (bus->seq) so does not need to be stored
@@ -117,6 +119,7 @@ struct spi_slave {
 #ifdef CONFIG_DM_SPI
 	struct udevice *dev;	/* struct spi_slave is dev->parentdata */
 	uint max_hz;
+	uint speed;
 	uint mode;
 #else
 	unsigned int bus;