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>

3 files changed, 212 insertions, 0 deletions

diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig
new file mode 100644
index 0000000000..a05b32d042
--- /dev/null
+++ b/drivers/i2c/muxes/Kconfig
@@ -0,0 +1,8 @@
+config I2C_MUX
+	bool "Suport I2C multiplexers"
+	depends on DM_I2C
+	help
+	  This enables I2C buses to be multiplexed, so that you can select
+	  one of several buses using some sort of control mechanism. The
+	  bus select is handled automatically when that bus is accessed,
+	  using a suitable I2C MUX driver.
diff --git a/drivers/i2c/muxes/Makefile b/drivers/i2c/muxes/Makefile
new file mode 100644
index 0000000000..7583e3a89b
--- /dev/null
+++ b/drivers/i2c/muxes/Makefile
@@ -0,0 +1,6 @@
+#
+# Copyright (c) 2015 Google, Inc
+#
+# SPDX-License-Identifier:	GPL-2.0+
+#
+obj-$(CONFIG_I2C_MUX) += i2c-mux-uclass.o
diff --git a/drivers/i2c/muxes/i2c-mux-uclass.c b/drivers/i2c/muxes/i2c-mux-uclass.c
new file mode 100644
index 0000000000..3f52bff2fb
--- /dev/null
+++ b/drivers/i2c/muxes/i2c-mux-uclass.c
@@ -0,0 +1,198 @@
+/*
+ * Copyright (c) 2015 Google, Inc
+ * Written by Simon Glass <sjg@chromium.org>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <errno.h>
+#include <i2c.h>
+#include <dm/lists.h>
+#include <dm/root.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+/**
+ * struct i2c_mux: Information the uclass stores about an I2C mux
+ *
+ * @selected:	Currently selected mux, or -1 for none
+ * @i2c_bus: I2C bus to use for communcation
+ */
+struct i2c_mux {
+	int selected;
+	struct udevice *i2c_bus;
+};
+
+/**
+ * struct i2c_mux_bus: Information about each bus the mux controls
+ *
+ * @channel: Channel number used to select this bus
+ */
+struct i2c_mux_bus {
+	uint channel;
+};
+
+/* Find out the mux channel number */
+static int i2c_mux_child_post_bind(struct udevice *dev)
+{
+	struct i2c_mux_bus *plat = dev_get_parent_platdata(dev);
+	int channel;
+
+	channel = fdtdec_get_int(gd->fdt_blob, dev->of_offset, "reg", -1);
+	if (channel < 0)
+		return -EINVAL;
+	plat->channel = channel;
+
+	return 0;
+}
+
+/* Find the I2C buses selected by this mux */
+static int i2c_mux_post_bind(struct udevice *mux)
+{
+	const void *blob = gd->fdt_blob;
+	int ret;
+	int offset;
+
+	debug("%s: %s\n", __func__, mux->name);
+	/*
+	 * There is no compatible string in the sub-nodes, so we must manually
+	 * bind these
+	 */
+	for (offset = fdt_first_subnode(blob, mux->of_offset);
+	     offset > 0;
+	     offset = fdt_next_subnode(blob, offset)) {
+		struct udevice *dev;
+		const char *name;
+
+		name = fdt_get_name(blob, offset, NULL);
+		ret = device_bind_driver_to_node(mux, "i2c_mux_bus_drv", name,
+						 offset, &dev);
+		debug("   - bind ret=%d, %s\n", ret, dev ? dev->name : NULL);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+/* Set up the mux ready for use */
+static int i2c_mux_post_probe(struct udevice *mux)
+{
+	struct i2c_mux *priv = dev_get_uclass_priv(mux);
+	int ret;
+
+	debug("%s: %s\n", __func__, mux->name);
+	priv->selected = -1;
+
+	ret = uclass_get_device_by_phandle(UCLASS_I2C, mux, "i2c-parent",
+					   &priv->i2c_bus);
+	if (ret)
+		return ret;
+	debug("%s: bus=%p/%s\n", __func__, priv->i2c_bus, priv->i2c_bus->name);
+
+	return 0;
+}
+
+int i2c_mux_select(struct udevice *dev)
+{
+	struct i2c_mux_bus *plat = dev_get_parent_platdata(dev);
+	struct udevice *mux = dev->parent;
+	struct i2c_mux_ops *ops = i2c_mux_get_ops(mux);
+
+	if (!ops->select)
+		return -ENOSYS;
+
+	return ops->select(mux, dev, plat->channel);
+}
+
+int i2c_mux_deselect(struct udevice *dev)
+{
+	struct i2c_mux_bus *plat = dev_get_parent_platdata(dev);
+	struct udevice *mux = dev->parent;
+	struct i2c_mux_ops *ops = i2c_mux_get_ops(mux);
+
+	if (!ops->deselect)
+		return -ENOSYS;
+
+	return ops->deselect(mux, dev, plat->channel);
+}
+
+static int i2c_mux_bus_set_bus_speed(struct udevice *dev, unsigned int speed)
+{
+	struct udevice *mux = dev->parent;
+	struct i2c_mux *priv = dev_get_uclass_priv(mux);
+	int ret, ret2;
+
+	ret = i2c_mux_select(dev);
+	if (ret)
+		return ret;
+	ret = dm_i2c_set_bus_speed(priv->i2c_bus, speed);
+	ret2 = i2c_mux_deselect(dev);
+
+	return ret ? ret : ret2;
+}
+
+static int i2c_mux_bus_probe(struct udevice *dev, uint chip_addr,
+			     uint chip_flags)
+{
+	struct udevice *mux = dev->parent;
+	struct i2c_mux *priv = dev_get_uclass_priv(mux);
+	struct dm_i2c_ops *ops = i2c_get_ops(priv->i2c_bus);
+	int ret, ret2;
+
+	debug("%s: %s, bus %s\n", __func__, dev->name, priv->i2c_bus->name);
+	if (!ops->probe_chip)
+		return -ENOSYS;
+	ret = i2c_mux_select(dev);
+	if (ret)
+		return ret;
+	ret = ops->probe_chip(priv->i2c_bus, chip_addr, chip_flags);
+	ret2 = i2c_mux_deselect(dev);
+
+	return ret ? ret : ret2;
+}
+
+static int i2c_mux_bus_xfer(struct udevice *dev, struct i2c_msg *msg,
+			    int nmsgs)
+{
+	struct udevice *mux = dev->parent;
+	struct i2c_mux *priv = dev_get_uclass_priv(mux);
+	struct dm_i2c_ops *ops = i2c_get_ops(priv->i2c_bus);
+	int ret, ret2;
+
+	debug("%s: %s, bus %s\n", __func__, dev->name, priv->i2c_bus->name);
+	if (!ops->xfer)
+		return -ENOSYS;
+	ret = i2c_mux_select(dev);
+	if (ret)
+		return ret;
+	ret = ops->xfer(priv->i2c_bus, msg, nmsgs);
+	ret2 = i2c_mux_deselect(dev);
+
+	return ret ? ret : ret2;
+}
+
+static const struct dm_i2c_ops i2c_mux_bus_ops = {
+	.xfer		= i2c_mux_bus_xfer,
+	.probe_chip	= i2c_mux_bus_probe,
+	.set_bus_speed	= i2c_mux_bus_set_bus_speed,
+};
+
+U_BOOT_DRIVER(i2c_mux_bus) = {
+	.name		= "i2c_mux_bus_drv",
+	.id		= UCLASS_I2C,
+	.per_child_auto_alloc_size = sizeof(struct dm_i2c_chip),
+	.ops	= &i2c_mux_bus_ops,
+};
+
+UCLASS_DRIVER(i2c_mux) = {
+	.id		= UCLASS_I2C_MUX,
+	.name		= "i2c_mux",
+	.post_bind	= i2c_mux_post_bind,
+	.post_probe	= i2c_mux_post_probe,
+	.per_device_auto_alloc_size = sizeof(struct i2c_mux),
+	.per_child_platdata_auto_alloc_size = sizeof(struct i2c_mux_bus),
+	.child_post_bind = i2c_mux_child_post_bind,
+};