i2c: mux: gpio: Add support for the 'settle-time-us' property

Some hardware need some time to switch from a bus to another. This can
cause the first transfers following the selection of a bus to fail.
There is no way to configure this kind of waiting time in the driver.

Add support for the 'settle-time-us' device-tree property. When set,
the i2c_mux_gpio_select() applies a delay before returning, leaving
enough time to the hardware to switch to the new bus.

Signed-off-by: Bastien Curutchet <[e-mail]>
Reviewed-by: Andi Shyti <[e-mail]>
Acked-by: Peter Rosin <[e-mail]>
Signed-off-by: Andi Shyti <[e-mail]>

drivers/i2c/muxes/i2c-mux-gpio.c

···
  */
 
 #include <linux/bits.h>
+#include <linux/delay.h>
 #include <linux/gpio/consumer.h>
 #include <linux/gpio/driver.h>
 #include <linux/i2c.h>
···
 	struct gpiomux *mux = i2c_mux_priv(muxc);
 
 	i2c_mux_gpio_set(mux, chan);
+
+	if (mux->data.settle_time)
+		fsleep(mux->data.settle_time);
 
 	return 0;
 }
···
 
 	if (device_property_read_u32(dev, "idle-state", &mux->data.idle))
 		mux->data.idle = I2C_MUX_GPIO_NO_IDLE;
+
+	device_property_read_u32(dev, "settle-time-us", &mux->data.settle_time);
 
 	return 0;
 }

include/linux/platform_data/i2c-mux-gpio.h

···
  *	position
  * @n_values: Number of multiplexer positions (busses to instantiate)
  * @idle: Bitmask to write to MUX when idle or GPIO_I2CMUX_NO_IDLE if not used
+ * @settle_time: Delay to wait when a new bus is selected
  */
 struct i2c_mux_gpio_platform_data {
 	int parent;
···
 	const unsigned *values;
 	int n_values;
 	unsigned idle;
+	u32 settle_time;
 };
 
 #endif /* _LINUX_I2C_MUX_GPIO_H */