dm: i2c: Add support for multiplexed I2C buses

Add a new I2C_MUX uclass. Devices in this class can multiplex between
several I2C buses, selecting them one at a time for use by the system.
The multiplexing mechanism is left to the driver to decide - it may be
controlled by GPIOs, for example.

The uclass supports only two methods: select() and deselect().

The current mux state is expected to be stored in the mux itself since
it is the only thing that knows how to make things work. The mux can
record the current state and then avoid switching unless it is necessary.
So select() can be skipped if the mux is already in the correct state.
Also deselect() can be made a nop if required.

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

1 files changed, 39 insertions, 0 deletions

diff --git a/include/i2c.h b/include/i2c.h
index d19182931c..6493931c35 100644
--- a/include/i2c.h
+++ b/include/i2c.h
@@ -445,6 +445,45 @@ struct dm_i2c_ops {
 #define i2c_get_ops(dev)	((struct dm_i2c_ops *)(dev)->driver->ops)
 
 /**
+ * struct i2c_mux_ops - operations for an I2C mux
+ *
+ * The current mux state is expected to be stored in the mux itself since
+ * it is the only thing that knows how to make things work. The mux can
+ * record the current state and then avoid switching unless it is necessary.
+ * So select() can be skipped if the mux is already in the correct state.
+ * Also deselect() can be made a nop if required.
+ */
+struct i2c_mux_ops {
+	/**
+	 * select() - select one of of I2C buses attached to a mux
+	 *
+	 * This will be called when there is no bus currently selected by the
+	 * mux. This method does not need to deselect the old bus since
+	 * deselect() will be already have been called if necessary.
+	 *
+	 * @mux:	Mux device
+	 * @bus:	I2C bus to select
+	 * @channel:	Channel number correponding to the bus to select
+	 * @return 0 if OK, -ve on error
+	 */
+	int (*select)(struct udevice *mux, struct udevice *bus, uint channel);
+
+	/**
+	 * deselect() - select one of of I2C buses attached to a mux
+	 *
+	 * This is used to deselect the currently selected I2C bus.
+	 *
+	 * @mux:	Mux device
+	 * @bus:	I2C bus to deselect
+	 * @channel:	Channel number correponding to the bus to deselect
+	 * @return 0 if OK, -ve on error
+	 */
+	int (*deselect)(struct udevice *mux, struct udevice *bus, uint channel);
+};
+
+#define i2c_mux_get_ops(dev)	((struct i2c_mux_ops *)(dev)->driver->ops)
+
+/**
  * i2c_get_chip() - get a device to use to access a chip on a bus
  *
  * This returns the device for the given chip address. The device can then