diff --git a/Documentation/i2c/index.rst b/Documentation/i2c/index.rst
index 6270f1fd7d4e..aaf33d1315f4 100644
--- a/Documentation/i2c/index.rst
+++ b/Documentation/i2c/index.rst
@@ -16,6 +16,7 @@ Introduction
instantiating-devices
busses/index
i2c-topology
+ muxes/i2c-atr
muxes/i2c-mux-gpio
i2c-sysfs
diff --git a/Documentation/i2c/muxes/i2c-atr.rst b/Documentation/i2c/muxes/i2c-atr.rst
new file mode 100644
index 000000000000..da226fd4de63
--- /dev/null
+++ b/Documentation/i2c/muxes/i2c-atr.rst
@@ -0,0 +1,97 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=====================
+Kernel driver i2c-atr
+=====================
+
+Author: Luca Ceresoli <luca@xxxxxxxxxxxxxxxx>
+Author: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
+
+Description
+-----------
+
+An I2C Address Translator (ATR) is a device with an I2C slave parent
+("upstream") port and N I2C master child ("downstream") ports, and
+forwards transactions from upstream to the appropriate downstream port
+with a modified slave address. The address used on the parent bus is
+called the "alias" and is (potentially) different from the physical
+slave address of the child bus. Address translation is done by the
+hardware.
+
+An ATR looks similar to an i2c-mux except:
+ - the address on the parent and child busses can be different
+ - there is normally no need to select the child port; the alias used on the
+ parent bus implies it
+
+The ATR functionality can be provided by a chip with many other
+features. This file provides a helper to implement an ATR within your
+driver.
+
+The ATR creates a new I2C "child" adapter on each child bus. Adding
+devices on the child bus ends up in invoking the driver code to select
+an available alias. Maintaining an appropriate pool of available aliases
+and picking one for each new device is up to the driver implementer. The
+ATR maintains an table of currently assigned alias and uses it to modify
+all I2C transactions directed to devices on the child buses.
+
+A typical example follows.
+
+Topology::
+
+ Slave X @ 0x10
+ .-----. |
+ .-----. | |---+---- B
+ | CPU |--A--| ATR |
+ `-----' | |---+---- C
+ `-----' |
+ Slave Y @ 0x10
+
+Alias table:
+
+A, B and C are three physical I2C busses, electrically independent from
+each other. The ATR receives the transactions initiated on bus A and
+propagates them on bus B or bus C or none depending on the device address
+in the transaction and based on the alias table.
+
+Alias table:
+
+.. table::
+
+ =============== =====
+ Client Alias
+ =============== =====
+ X (bus B, 0x10) 0x20
+ Y (bus C, 0x10) 0x30
+ =============== =====
+
+Transaction:
+
+ - Slave X driver sends a transaction (on adapter B), slave address 0x10
+ - ATR driver finds slave X is on bus B and has alias 0x20, rewrites
+ messages with address 0x20, forwards to adapter A
+ - Physical I2C transaction on bus A, slave address 0x20
+ - ATR chip detects transaction on address 0x20, finds it in table,
+ propagates transaction on bus B with address translated to 0x10,
+ keeps clock streched on bus A waiting for reply
+ - Slave X chip (on bus B) detects transaction at its own physical
+ address 0x10 and replies normally
+ - ATR chip stops clock stretching and forwards reply on bus A,
+ with address translated back to 0x20
+ - ATR driver receives the reply, rewrites messages with address 0x10
+ as they were initially
+ - Slave X driver gets back the msgs[], with reply and address 0x10
+
+Usage:
+
+ 1. In your driver (typically in the probe function) add an ATR by
+ calling i2c_atr_new() passing your attach/detach callbacks
+ 2. When the attach callback is called pick an appropriate alias,
+ configure it in your chip and return the chosen alias in the
+ alias_id parameter
+ 3. When the detach callback is called, deconfigure the alias from
+ your chip and put it back in the pool for later usage
+
+I2C ATR functions and data structures
+-------------------------------------
+
+.. kernel-doc:: include/linux/i2c-atr.h
diff --git a/MAINTAINERS b/MAINTAINERS
index 7f4678dba495..375e13ee05a2 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -9688,6 +9688,14 @@ L: linux-acpi@xxxxxxxxxxxxxxx
S: Maintained
F: drivers/i2c/i2c-core-acpi.c
+I2C ADDRESS TRANSLATOR (ATR)
+M: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
+R: Luca Ceresoli <luca.ceresoli@xxxxxxxxxxx>
+L: linux-i2c@xxxxxxxxxxxxxxx
+S: Maintained
+F: drivers/i2c/i2c-atr.c
+F: include/linux/i2c-atr.h
+
I2C CONTROLLER DRIVER FOR NVIDIA GPU
M: Ajay Gupta <ajayg@xxxxxxxxxx>
L: linux-i2c@xxxxxxxxxxxxxxx
diff --git a/drivers/i2c/Kconfig b/drivers/i2c/Kconfig
index 438905e2a1d0..c6d1a345ea6d 100644
--- a/drivers/i2c/Kconfig
+++ b/drivers/i2c/Kconfig
@@ -71,6 +71,15 @@ config I2C_MUX
source "drivers/i2c/muxes/Kconfig"
+config I2C_ATR
+ tristate "I2C Address Translator (ATR) support"
+ help
+ Enable support for I2C Address Translator (ATR) chips.
+
+ An ATR allows accessing multiple I2C busses from a single
+ physical bus via address translation instead of bus selection as
+ i2c-muxes do.
+
config I2C_HELPER_AUTO
bool "Autoselect pertinent helper modules"
default y
diff --git a/drivers/i2c/Makefile b/drivers/i2c/Makefile
index c1d493dc9bac..3f71ce4711e3 100644
--- a/drivers/i2c/Makefile
+++ b/drivers/i2c/Makefile
@@ -13,6 +13,7 @@ i2c-core-$(CONFIG_OF) += i2c-core-of.o
obj-$(CONFIG_I2C_SMBUS) += i2c-smbus.o
obj-$(CONFIG_I2C_CHARDEV) += i2c-dev.o
obj-$(CONFIG_I2C_MUX) += i2c-mux.o
+obj-$(CONFIG_I2C_ATR) += i2c-atr.o
obj-y += algos/ busses/ muxes/
obj-$(CONFIG_I2C_STUB) += i2c-stub.o
obj-$(CONFIG_I2C_SLAVE_EEPROM) += i2c-slave-eeprom.o
diff --git a/drivers/i2c/i2c-atr.c b/drivers/i2c/i2c-atr.c
new file mode 100644
index 000000000000..5ab890b83670
--- /dev/null
+++ b/drivers/i2c/i2c-atr.c
@@ -0,0 +1,548 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * I2C Address Translator
+ *
+ * Copyright (c) 2019,2022 Luca Ceresoli <luca@xxxxxxxxxxxxxxxx>
+ * Copyright (c) 2022,2023 Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
+ *
+ * Originally based on i2c-mux.c
+ */
+
+#include <linux/fwnode.h>
+#include <linux/i2c-atr.h>
+#include <linux/i2c.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+
+#define ATR_MAX_ADAPTERS 100 /* Just a sanity limit */
+#define ATR_MAX_SYMLINK_LEN 11 /* Longest name is 10 chars: "channel-99" */
+
+/**
+ * struct i2c_atr_cli2alias_pair - Holds the alias assigned to a client.
+ * @node: List node
+ * @client: Pointer to the client on the child bus
+ * @alias: I2C alias address assigned by the driver.
+ * This is the address that will be used to issue I2C transactions
+ * on the parent (physical) bus.
+ */
+struct i2c_atr_cli2alias_pair {
+ struct list_head node;
+ const struct i2c_client *client;
+ u16 alias;
+};
+
+/**
+ * struct i2c_atr_chan - Data for a channel.
+ * @adap: The &struct i2c_adapter for the channel
+ * @atr: The parent I2C ATR
+ * @chan_id: The ID of this channel
+ * @alias_list: List of @struct i2c_atr_cli2alias_pair containing the
+ * assigned aliases
+ * @orig_addrs_lock: Mutex protecting @orig_addrs
+ * @orig_addrs: Buffer used to store the original addresses during transmit
+ * @orig_addrs_size: Size of @orig_addrs
+ */
+struct i2c_atr_chan {
+ struct i2c_adapter adap;
+ struct i2c_atr *atr;
+ u32 chan_id;
+
+ struct list_head alias_list;
+
+ /* Lock orig_addrs during xfer */
+ struct mutex orig_addrs_lock;
+ u16 *orig_addrs;
+ unsigned int orig_addrs_size;
+};
+
+/**
+ * struct i2c_atr - The I2C ATR instance
+ * @parent: The parent &struct i2c_adapter
+ * @dev: The device that owns the I2C ATR instance
+ * @ops: &struct i2c_atr_ops
+ * @priv: Private driver data, set with i2c_atr_set_driver_data()
+ * @algo: The &struct i2c_algorithm for adapters
+ * @lock: Lock for the I2C bus segment (see &struct i2c_lock_operations)
+ * @max_adapters: Maximum number of adapters this I2C ATR can have
+ * @adapter: Array of adapters
+ */
+struct i2c_atr {
+ struct i2c_adapter *parent;
+ struct device *dev;
+ const struct i2c_atr_ops *ops;
+
+ void *priv;
+
+ struct i2c_algorithm algo;
+ /* lock for the I2C bus segment (see struct i2c_lock_operations) */
+ struct mutex lock;
+ int max_adapters;
+
+ struct notifier_block i2c_nb;
+
+ struct i2c_adapter *adapter[];
+};
+
+static struct i2c_atr_cli2alias_pair *
+i2c_atr_find_mapping_by_client(const struct list_head *list,
+ const struct i2c_client *client)
+{
+ struct i2c_atr_cli2alias_pair *c2a;
+
+ list_for_each_entry(c2a, list, node) {
+ if (c2a->client == client)
+ return c2a;
+ }
+
+ return NULL;
+}
+
+static struct i2c_atr_cli2alias_pair *
+i2c_atr_find_mapping_by_addr(const struct list_head *list, u16 phys_addr)
+{
+ struct i2c_atr_cli2alias_pair *c2a;
+
+ list_for_each_entry(c2a, list, node) {
+ if (c2a->client->addr == phys_addr)
+ return c2a;
+ }
+
+ return NULL;
+}
+
+/*
+ * Replace all message addresses with their aliases, saving the original
+ * addresses.
+ *
+ * This function is internal for use in i2c_atr_master_xfer(). It must be
+ * followed by i2c_atr_unmap_msgs() to restore the original addresses.
+ */
+static int i2c_atr_map_msgs(struct i2c_atr_chan *chan, struct i2c_msg *msgs,
+ int num)
+{
+ struct i2c_atr *atr = chan->atr;
+ static struct i2c_atr_cli2alias_pair *c2a;
+ int i;
+
+ /* Ensure we have enough room to save the original addresses */
+ if (unlikely(chan->orig_addrs_size < num)) {
+ u16 *new_buf;
+
+ /* We don't care about old data, hence no realloc() */
+ new_buf = kmalloc_array(num, sizeof(*new_buf), GFP_KERNEL);
+ if (!new_buf)
+ return -ENOMEM;
+
+ kfree(chan->orig_addrs);
+ chan->orig_addrs = new_buf;
+ chan->orig_addrs_size = num;
+ }
+
+ for (i = 0; i < num; i++) {
+ chan->orig_addrs[i] = msgs[i].addr;
+
+ c2a = i2c_atr_find_mapping_by_addr(&chan->alias_list,
+ msgs[i].addr);
+ if (!c2a) {
+ dev_err(atr->dev, "client 0x%02x not mapped!\n",
+ msgs[i].addr);
+ return -ENXIO;
+ }
+
+ msgs[i].addr = c2a->alias;
+ }
+
+ return 0;
+}
+
+/*
+ * Restore all message address aliases with the original addresses. This
+ * function is internal for use in i2c_atr_master_xfer().
+ *
+ * @see i2c_atr_map_msgs()
+ */
+static void i2c_atr_unmap_msgs(struct i2c_atr_chan *chan, struct i2c_msg *msgs,
+ int num)
+{
+ int i;
+
+ for (i = 0; i < num; i++)
+ msgs[i].addr = chan->orig_addrs[i];
+}
+
+static int i2c_atr_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
+ int num)
+{
+ struct i2c_atr_chan *chan = adap->algo_data;
+ struct i2c_atr *atr = chan->atr;
+ struct i2c_adapter *parent = atr->parent;
+ int ret;
+
+ /* Translate addresses */
+ mutex_lock(&chan->orig_addrs_lock);
+
+ ret = i2c_atr_map_msgs(chan, msgs, num);
+ if (ret < 0)
+ goto err_unlock;
+
+ /* Perform the transfer */
+ ret = i2c_transfer(parent, msgs, num);
+
+ /* Restore addresses */
+ i2c_atr_unmap_msgs(chan, msgs, num);
+
+err_unlock:
+ mutex_unlock(&chan->orig_addrs_lock);
+
+ return ret;
+}
+
+static int i2c_atr_smbus_xfer(struct i2c_adapter *adap, u16 addr,
+ unsigned short flags, char read_write, u8 command,
+ int size, union i2c_smbus_data *data)
+{
+ struct i2c_atr_chan *chan = adap->algo_data;
+ struct i2c_atr *atr = chan->atr;
+ struct i2c_adapter *parent = atr->parent;
+ struct i2c_atr_cli2alias_pair *c2a;
+
+ c2a = i2c_atr_find_mapping_by_addr(&chan->alias_list, addr);
+ if (!c2a) {
+ dev_err(atr->dev, "client 0x%02x not mapped!\n", addr);
+ return -ENXIO;
+ }
+
+ return i2c_smbus_xfer(parent, c2a->alias, flags, read_write, command,
+ size, data);
+}
+
+static u32 i2c_atr_functionality(struct i2c_adapter *adap)
+{
+ struct i2c_atr_chan *chan = adap->algo_data;
+ struct i2c_adapter *parent = chan->atr->parent;
+
+ return parent->algo->functionality(parent);
+}
+
+static void i2c_atr_lock_bus(struct i2c_adapter *adapter, unsigned int flags)
+{
+ struct i2c_atr_chan *chan = adapter->algo_data;
+ struct i2c_atr *atr = chan->atr;
+
+ mutex_lock(&atr->lock);
+}
+
+static int i2c_atr_trylock_bus(struct i2c_adapter *adapter, unsigned int flags)
+{
+ struct i2c_atr_chan *chan = adapter->algo_data;
+ struct i2c_atr *atr = chan->atr;
+
+ return mutex_trylock(&atr->lock);
+}
+
+static void i2c_atr_unlock_bus(struct i2c_adapter *adapter, unsigned int flags)
+{
+ struct i2c_atr_chan *chan = adapter->algo_data;
+ struct i2c_atr *atr = chan->atr;
+
+ mutex_unlock(&atr->lock);
+}
+
+static const struct i2c_lock_operations i2c_atr_lock_ops = {
+ .lock_bus = i2c_atr_lock_bus,
+ .trylock_bus = i2c_atr_trylock_bus,
+ .unlock_bus = i2c_atr_unlock_bus,
+};
+
+static int i2c_atr_attach_client(struct i2c_adapter *adapter,
+ const struct i2c_client *client)
+{
+ struct i2c_atr_chan *chan = adapter->algo_data;
+ struct i2c_atr *atr = chan->atr;
+ struct i2c_atr_cli2alias_pair *c2a;
+ u16 alias_id;
+ int ret;
+
+ c2a = kzalloc(sizeof(*c2a), GFP_KERNEL);
+ if (!c2a)
+ return -ENOMEM;
+
+ ret = atr->ops->attach_client(atr, chan->chan_id, client, &alias_id);
+ if (ret)
+ goto err_free;
+
+ dev_dbg(atr->dev, "chan%u: client 0x%02x mapped at alias 0x%02x (%s)\n",
+ chan->chan_id, client->addr, alias_id, client->name);
+
+ c2a->client = client;
+ c2a->alias = alias_id;
+ list_add(&c2a->node, &chan->alias_list);
+
+ return 0;
+
+err_free:
+ kfree(c2a);
+
+ return ret;
+}
+
+static void i2c_atr_detach_client(struct i2c_adapter *adapter,
+ const struct i2c_client *client)
+{
+ struct i2c_atr_chan *chan = adapter->algo_data;
+ struct i2c_atr *atr = chan->atr;
+ struct i2c_atr_cli2alias_pair *c2a;
+
+ atr->ops->detach_client(atr, chan->chan_id, client);
+
+ c2a = i2c_atr_find_mapping_by_client(&chan->alias_list, client);
+ if (!c2a) {
+ /* This should never happen */
+ dev_warn(atr->dev, "Unable to find address mapping\n");
+ return;
+ }
+
+ dev_dbg(atr->dev,
+ "chan%u: client 0x%02x unmapped from alias 0x%02x (%s)\n",
+ chan->chan_id, client->addr, c2a->alias, client->name);
+
+ list_del(&c2a->node);
+ kfree(c2a);
+}
+
+static int i2c_atr_bus_notifier_call(struct notifier_block *nb,
+ unsigned long event, void *device)
+{
+ struct i2c_atr *atr = container_of(nb, struct i2c_atr, i2c_nb);
+ struct device *dev = device;
+ struct i2c_client *client;
+ u32 chan_id;
+ int ret;
+
+ client = i2c_verify_client(dev);
+ if (!client)
+ return NOTIFY_DONE;
+
+ /* Is the client in one of our adapters? */
+ for (chan_id = 0; chan_id < atr->max_adapters; ++chan_id) {
+ if (client->adapter == atr->adapter[chan_id])
+ break;
+ }
+
+ if (chan_id == atr->max_adapters)
+ return NOTIFY_DONE;
+
+ switch (event) {
+ case BUS_NOTIFY_ADD_DEVICE:
+ ret = i2c_atr_attach_client(client->adapter, client);
+ if (ret)
+ dev_err(atr->dev,
+ "Failed to attach remote client '%s': %d\n",
+ dev_name(dev), ret);
+ break;
+
+ case BUS_NOTIFY_DEL_DEVICE:
+ i2c_atr_detach_client(client->adapter, client);
+ break;
+
+ default:
+ break;
+ }
+
+ return NOTIFY_DONE;
+}
+
+struct i2c_atr *i2c_atr_new(struct i2c_adapter *parent, struct device *dev,
+ const struct i2c_atr_ops *ops, int max_adapters)
+{
+ struct i2c_atr *atr;
+ int ret;
+
+ if (max_adapters > ATR_MAX_ADAPTERS)
+ return ERR_PTR(-EINVAL);
+
+ if (!ops || !ops->attach_client || !ops->detach_client)
+ return ERR_PTR(-EINVAL);
+
+ atr = kzalloc(struct_size(atr, adapter, max_adapters), GFP_KERNEL);
+ if (!atr)
+ return ERR_PTR(-ENOMEM);
+
+ mutex_init(&atr->lock);
+
+ atr->parent = parent;
+ atr->dev = dev;
+ atr->ops = ops;
+ atr->max_adapters = max_adapters;
+
+ if (parent->algo->master_xfer)
+ atr->algo.master_xfer = i2c_atr_master_xfer;
+ if (parent->algo->smbus_xfer)
+ atr->algo.smbus_xfer = i2c_atr_smbus_xfer;
+ atr->algo.functionality = i2c_atr_functionality;
+
+ atr->i2c_nb.notifier_call = i2c_atr_bus_notifier_call;
+ ret = bus_register_notifier(&i2c_bus_type, &atr->i2c_nb);
+ if (ret) {
+ mutex_destroy(&atr->lock);
+ return ERR_PTR(ret);
+ }
+
+ return atr;
+}
+EXPORT_SYMBOL_NS_GPL(i2c_atr_new, I2C_ATR);
+
+void i2c_atr_delete(struct i2c_atr *atr)
+{
+ bus_unregister_notifier(&i2c_bus_type, &atr->i2c_nb);
+ mutex_destroy(&atr->lock);
+ kfree(atr);
+}
+EXPORT_SYMBOL_NS_GPL(i2c_atr_delete, I2C_ATR);
+
+int i2c_atr_add_adapter(struct i2c_atr *atr, u32 chan_id,
+ struct device *adapter_parent,
+ struct fwnode_handle *bus_handle)
+{
+ struct i2c_adapter *parent = atr->parent;
+ struct device *dev = atr->dev;
+ struct i2c_atr_chan *chan;
+ char symlink_name[ATR_MAX_SYMLINK_LEN];
+ int ret;
+
+ if (chan_id >= atr->max_adapters) {
+ dev_err(dev, "No room for more i2c-atr adapters\n");
+ return -EINVAL;
+ }
+
+ if (atr->adapter[chan_id]) {
+ dev_err(dev, "Adapter %d already present\n", chan_id);
+ return -EEXIST;
+ }
+
+ chan = kzalloc(sizeof(*chan), GFP_KERNEL);
+ if (!chan)
+ return -ENOMEM;
+
+ if (!adapter_parent)
+ adapter_parent = dev;
+
+ chan->atr = atr;
+ chan->chan_id = chan_id;
+ INIT_LIST_HEAD(&chan->alias_list);
+ mutex_init(&chan->orig_addrs_lock);
+
+ snprintf(chan->adap.name, sizeof(chan->adap.name), "i2c-%d-atr-%d",
+ i2c_adapter_id(parent), chan_id);
+ chan->adap.owner = THIS_MODULE;
+ chan->adap.algo = &atr->algo;
+ chan->adap.algo_data = chan;
+ chan->adap.dev.parent = adapter_parent;
+ chan->adap.retries = parent->retries;
+ chan->adap.timeout = parent->timeout;
+ chan->adap.quirks = parent->quirks;
+ chan->adap.lock_ops = &i2c_atr_lock_ops;
+
+ if (bus_handle) {
+ device_set_node(&chan->adap.dev, fwnode_handle_get(bus_handle));
+ } else {
+ struct fwnode_handle *atr_node;
+ struct fwnode_handle *child;
+ u32 reg;
+
+ atr_node = device_get_named_child_node(dev, "i2c-atr");
+
+ fwnode_for_each_child_node(atr_node, child) {
+ ret = fwnode_property_read_u32(child, "reg", ®);
+ if (ret)
+ continue;
+ if (chan_id == reg)
+ break;
+ }
+
+ device_set_node(&chan->adap.dev, child);
+ fwnode_handle_put(atr_node);
+ }
+
+ atr->adapter[chan_id] = &chan->adap;
+
+ ret = i2c_add_adapter(&chan->adap);
+ if (ret) {
+ dev_err(dev, "failed to add atr-adapter %u (error=%d)\n",
+ chan_id, ret);
+ goto err_fwnode_put;
+ }
+
+ snprintf(symlink_name, sizeof(symlink_name), "channel-%u",
+ chan->chan_id);
+
+ ret = sysfs_create_link(&chan->adap.dev.kobj, &dev->kobj, "atr_device");
+ if (ret)
+ dev_warn(dev, "can't create symlink to atr device\n");
+ ret = sysfs_create_link(&dev->kobj, &chan->adap.dev.kobj, symlink_name);
+ if (ret)
+ dev_warn(dev, "can't create symlink for channel %u\n", chan_id);
+
+ dev_dbg(dev, "Added ATR child bus %d\n", i2c_adapter_id(&chan->adap));
+
+ return 0;
+
+err_fwnode_put:
+ fwnode_handle_put(dev_fwnode(&chan->adap.dev));
+ mutex_destroy(&chan->orig_addrs_lock);
+ kfree(chan);
+ return ret;
+}
+EXPORT_SYMBOL_NS_GPL(i2c_atr_add_adapter, I2C_ATR);
+
+void i2c_atr_del_adapter(struct i2c_atr *atr, u32 chan_id)
+{
+ char symlink_name[ATR_MAX_SYMLINK_LEN];
+ struct i2c_adapter *adap;
+ struct i2c_atr_chan *chan;
+ struct fwnode_handle *fwnode;
+ struct device *dev = atr->dev;
+
+ adap = atr->adapter[chan_id];
+ if (!adap)
+ return;
+
+ chan = adap->algo_data;
+ fwnode = dev_fwnode(&adap->dev);
+
+ dev_dbg(dev, "Removing ATR child bus %d\n", i2c_adapter_id(adap));
+
+ snprintf(symlink_name, sizeof(symlink_name), "channel-%u",
+ chan->chan_id);
+ sysfs_remove_link(&dev->kobj, symlink_name);
+ sysfs_remove_link(&chan->adap.dev.kobj, "atr_device");
+
+ i2c_del_adapter(adap);
+
+ atr->adapter[chan_id] = NULL;
+
+ fwnode_handle_put(fwnode);
+ mutex_destroy(&chan->orig_addrs_lock);
+ kfree(chan->orig_addrs);
+ kfree(chan);
+}
+EXPORT_SYMBOL_NS_GPL(i2c_atr_del_adapter, I2C_ATR);
+
+void i2c_atr_set_driver_data(struct i2c_atr *atr, void *data)
+{
+ atr->priv = data;
+}
+EXPORT_SYMBOL_NS_GPL(i2c_atr_set_driver_data, I2C_ATR);
+
+void *i2c_atr_get_driver_data(struct i2c_atr *atr)
+{
+ return atr->priv;
+}
+EXPORT_SYMBOL_NS_GPL(i2c_atr_get_driver_data, I2C_ATR);
+
+MODULE_AUTHOR("Luca Ceresoli <luca.ceresoli@xxxxxxxxxxx>");
+MODULE_AUTHOR("Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("I2C Address Translator");
+MODULE_LICENSE("GPL");
diff --git a/include/linux/i2c-atr.h b/include/linux/i2c-atr.h
new file mode 100644
index 000000000000..7596f70ce1ab
--- /dev/null
+++ b/include/linux/i2c-atr.h
@@ -0,0 +1,116 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * I2C Address Translator
+ *
+ * Copyright (c) 2019,2022 Luca Ceresoli <luca@xxxxxxxxxxxxxxxx>
+ * Copyright (c) 2022,2023 Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
+ *
+ * Based on i2c-mux.h
+ */
+
+#ifndef _LINUX_I2C_ATR_H
+#define _LINUX_I2C_ATR_H
+
+#include <linux/i2c.h>
+#include <linux/types.h>
+
+struct device;
+struct fwnode_handle;
+struct i2c_atr;
+
+/**
+ * struct i2c_atr_ops - Callbacks from ATR to the device driver.
+ * @attach_client: Notify the driver of a new device connected on a child
+ * bus. The driver must choose an I2C alias, configure the
+ * hardware to use it and return it in `alias_id`.
+ * @detach_client: Notify the driver of a device getting disconnected. The
+ * driver must configure the hardware to stop using the
+ * alias.
+ *
+ * All these functions return 0 on success, a negative error code otherwise.
+ */
+struct i2c_atr_ops {
+ int (*attach_client)(struct i2c_atr *atr, u32 chan_id,
+ const struct i2c_client *client, u16 *alias_id);
+ void (*detach_client)(struct i2c_atr *atr, u32 chan_id,
+ const struct i2c_client *client);
+};
+
+/**
+ * i2c_atr_new() - Allocate and initialize an I2C ATR helper.
+ * @parent: The parent (upstream) adapter
+ * @dev: The device acting as an ATR
+ * @ops: Driver-specific callbacks
+ * @max_adapters: Maximum number of child adapters
+ *
+ * The new ATR helper is connected to the parent adapter but has no child
+ * adapters. Call i2c_atr_add_adapter() to add some.
+ *
+ * Call i2c_atr_delete() to remove.
+ *
+ * Return: pointer to the new ATR helper object, or ERR_PTR
+ */
+struct i2c_atr *i2c_atr_new(struct i2c_adapter *parent, struct device *dev,
+ const struct i2c_atr_ops *ops, int max_adapters);
+
+/**
+ * i2c_atr_delete - Delete an I2C ATR helper.
+ * @atr: I2C ATR helper to be deleted.
+ *
+ * Precondition: all the adapters added with i2c_atr_add_adapter() mumst be
+ * removed by calling i2c_atr_del_adapter().
+ */
+void i2c_atr_delete(struct i2c_atr *atr);
+
+/**
+ * i2c_atr_add_adapter - Create a child ("downstream") I2C bus.
+ * @atr: The I2C ATR
+ * @chan_id: Index of the new adapter (0 .. max_adapters-1). This value is
+ * passed to the callbacks in `struct i2c_atr_ops`.
+ * @adapter_parent: The device used as the parent of the new i2c adapter, or NULL
+ * to use the i2c-atr device as the parent.
+ * @bus_handle: The fwnode handle that points to the adapter's i2c
+ * peripherals, or NULL.
+ *
+ * After calling this function a new i2c bus will appear. Adding and removing
+ * devices on the downstream bus will result in calls to the
+ * &i2c_atr_ops->attach_client and &i2c_atr_ops->detach_client callbacks for the
+ * driver to assign an alias to the device.
+ *
+ * The adapter's fwnode is set to @bus_handle, or if @bus_handle is NULL the
+ * function looks for a child node whose 'reg' property matches the chan_id
+ * under the i2c-atr device's 'i2c-atr' node.
+ *
+ * Call i2c_atr_del_adapter() to remove the adapter.
+ *
+ * Return: 0 on success, a negative error code otherwise.
+ */
+int i2c_atr_add_adapter(struct i2c_atr *atr, u32 chan_id,
+ struct device *adapter_parent,
+ struct fwnode_handle *bus_handle);
+
+/**
+ * i2c_atr_del_adapter - Remove a child ("downstream") I2C bus added by
+ * i2c_atr_add_adapter(). If no I2C bus has been added
+ * this function is a no-op.
+ * @atr: The I2C ATR
+ * @chan_id: Index of the adapter to be removed (0 .. max_adapters-1)
+ */
+void i2c_atr_del_adapter(struct i2c_atr *atr, u32 chan_id);
+
+/**
+ * i2c_atr_set_driver_data - Set private driver data to the i2c-atr instance.
+ * @atr: The I2C ATR
+ * @data: Pointer to the data to store
+ */
+void i2c_atr_set_driver_data(struct i2c_atr *atr, void *data);
+
+/**
+ * i2c_atr_get_driver_data - Get the stored drive data.
+ * @atr: The I2C ATR
+ *
+ * Return: Pointer to the stored data
+ */
+void *i2c_atr_get_driver_data(struct i2c_atr *atr);
+
+#endif /* _LINUX_I2C_ATR_H */
