Convert the device-tree parsing path to the generic fwnode/device
property accessors so the driver can be probed on ACPI and swnode
platforms as well as OF. The helper is renamed from
i2c_mux_reg_probe_dt() to i2c_mux_reg_probe_fw() to reflect that.

Accessor translation:

  of_parse_phandle("i2c-parent") +
    of_find_i2c_adapter_by_node()    -> fwnode_find_reference() +
                                         i2c_get_adapter_by_fwnode()
  of_get_child_count()               -> device_get_child_node_count()
  of_property_read_bool()            -> device_property_read_bool()
  for_each_child_of_node()           -> device_for_each_child_node()
    of_property_read_u32("reg")        on OF:   fwnode_property_read_u32()
                                       on ACPI: acpi_get_local_address()
  of_property_read_u32("idle-state") -> device_property_read_u32()

Behavioural preservations (deliberate, to avoid regressing existing
users):

  - The three-way endian fallback is kept verbatim: an explicit
    "little-endian" property wins, then "big-endian", and otherwise
    the host's compile-time byte order. device_is_big_endian() is
    not used here because it ignores "little-endian" and introduces
    "native-endian" semantics, which would diverge from the binding.

  - The platform-resource fallback for an un-mapped reg keeps its
    "if (!mux->data.reg)" guard so a platdata user that supplies a
    pre-ioremapped reg through struct i2c_mux_reg_platform_data is
    not clobbered.

The OF-only of_address_to_resource() translation in the old
probe_dt() is dropped because the same address is available from
the platform_device resource table on both OF and ACPI, and the
existing fallback in probe() ioremaps it.

Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
---
Convert the device-tree parsing path in i2c-mux-reg to the generic
fwnode/device property accessors so the driver can be probed on ACPI
and swnode platforms in addition to OF.

Changes in v2 (per Peter's review of v1 [1]):

- Restore the three-way endian-property fallback verbatim. v1 used
  device_is_big_endian(), which ignores "little-endian" and adds
  "native-endian" semantics — a binding-visible behaviour change on
  big-endian hosts that did not specify the property. v2 keeps the
  original logic ("little-endian" wins, then "big-endian", else the
  host's compile-time byte order), expressed via
  device_property_read_bool() instead of of_property_read_bool().

- Restore the "if (!mux->data.reg)" guard around
  devm_platform_get_and_ioremap_resource() in probe(). v1 dropped it
  and would have clobbered the pre-ioremapped reg supplied by a
  platdata user through struct i2c_mux_reg_platform_data.

- Restore the dev_err_probe() wrapper at the probe_fw() call site so
  the silent error paths in the helper still produce a dmesg line on
  failure.

- Rewrite the changelog to enumerate the accessor translations, the
  new ACPI child-node handling via acpi_get_local_address(), and the
  behavioural preservations above.

Tested locally on the ACPI/non-OF code path I added. I do not have
any of the in-tree DT users of i2c-mux-reg on hand (the existing
boards are on PowerPC and SH), so I have not been able to verify
that the OF path is byte-for-byte unchanged in behaviour at runtime.
Tested-by tags from anyone running this driver on a current DT
board would be very welcome.

[1] https://lore.kernel.org/r/20260115003523.26660-1-abdurrahman@nexthop.ai
---
 drivers/i2c/muxes/i2c-mux-reg.c | 84 +++++++++++++++--------------------------
 1 file changed, 31 insertions(+), 53 deletions(-)

diff --git a/drivers/i2c/muxes/i2c-mux-reg.c b/drivers/i2c/muxes/i2c-mux-reg.c
index 1e566ea92bc9..5a7ee763606c 100644
--- a/drivers/i2c/muxes/i2c-mux-reg.c
+++ b/drivers/i2c/muxes/i2c-mux-reg.c
@@ -11,7 +11,6 @@
 #include <linux/init.h>
 #include <linux/io.h>
 #include <linux/module.h>
-#include <linux/of_address.h>
 #include <linux/platform_data/i2c-mux-reg.h>
 #include <linux/platform_device.h>
 #include <linux/slab.h>
@@ -75,83 +74,64 @@ static int i2c_mux_reg_deselect(struct i2c_mux_core *muxc, u32 chan)
 	return 0;
 }
 
-#ifdef CONFIG_OF
-static int i2c_mux_reg_probe_dt(struct regmux *mux,
-				struct platform_device *pdev)
+static int i2c_mux_reg_probe_fw(struct regmux *mux, struct device *dev)
 {
-	struct device_node *np = pdev->dev.of_node;
-	struct device_node *adapter_np, *child;
+	struct fwnode_handle *fwnode, *child;
 	struct i2c_adapter *adapter;
-	struct resource res;
 	unsigned *values;
-	int i = 0;
+	int ret, i = 0;
 
-	if (!np)
+	if (!dev_fwnode(dev))
 		return -ENODEV;
 
-	adapter_np = of_parse_phandle(np, "i2c-parent", 0);
-	if (!adapter_np) {
-		dev_err(&pdev->dev, "Cannot parse i2c-parent\n");
+	fwnode = fwnode_find_reference(dev_fwnode(dev), "i2c-parent", 0);
+	if (IS_ERR(fwnode)) {
+		dev_err(dev, "missing 'i2c-parent' property\n");
 		return -ENODEV;
 	}
-	adapter = of_find_i2c_adapter_by_node(adapter_np);
-	of_node_put(adapter_np);
+
+	adapter = i2c_get_adapter_by_fwnode(fwnode);
+	fwnode_handle_put(fwnode);
 	if (!adapter)
 		return -EPROBE_DEFER;
 
 	mux->data.parent = i2c_adapter_id(adapter);
 	put_device(&adapter->dev);
 
-	mux->data.n_values = of_get_child_count(np);
-	if (of_property_read_bool(np, "little-endian")) {
-		mux->data.little_endian = true;
-	} else if (of_property_read_bool(np, "big-endian")) {
-		mux->data.little_endian = false;
-	} else {
-#if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : \
-	defined(__LITTLE_ENDIAN)
+	mux->data.n_values = device_get_child_node_count(dev);
+	if (device_property_read_bool(dev, "little-endian"))
 		mux->data.little_endian = true;
-#elif defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : \
-	defined(__BIG_ENDIAN)
+	else if (device_property_read_bool(dev, "big-endian"))
 		mux->data.little_endian = false;
-#else
-#error Endianness not defined?
-#endif
-	}
-	mux->data.write_only = of_property_read_bool(np, "write-only");
+	else
+		mux->data.little_endian = IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN);
+	mux->data.write_only = device_property_read_bool(dev, "write-only");
 
-	values = devm_kcalloc(&pdev->dev,
-			      mux->data.n_values, sizeof(*mux->data.values),
+	values = devm_kcalloc(dev, mux->data.n_values, sizeof(*mux->data.values),
 			      GFP_KERNEL);
 	if (!values)
 		return -ENOMEM;
 
-	for_each_child_of_node(np, child) {
-		of_property_read_u32(child, "reg", values + i);
+	device_for_each_child_node(dev, child) {
+		if (is_of_node(child)) {
+			fwnode_property_read_u32(child, "reg", values + i);
+		} else if (is_acpi_node(child)) {
+			ret = acpi_get_local_address(ACPI_HANDLE_FWNODE(child), values + i);
+			if (ret) {
+				fwnode_handle_put(child);
+				return dev_err_probe(dev, ret, "Cannot get address\n");
+			}
+		}
+
 		i++;
 	}
 	mux->data.values = values;
 
-	if (!of_property_read_u32(np, "idle-state", &mux->data.idle))
+	if (!device_property_read_u32(dev, "idle-state", &mux->data.idle))
 		mux->data.idle_in_use = true;
 
-	/* map address from "reg" if exists */
-	if (of_address_to_resource(np, 0, &res) == 0) {
-		mux->data.reg_size = resource_size(&res);
-		mux->data.reg = devm_ioremap_resource(&pdev->dev, &res);
-		if (IS_ERR(mux->data.reg))
-			return PTR_ERR(mux->data.reg);
-	}
-
-	return 0;
-}
-#else
-static int i2c_mux_reg_probe_dt(struct regmux *mux,
-				struct platform_device *pdev)
-{
 	return 0;
 }
-#endif
 
 static int i2c_mux_reg_probe(struct platform_device *pdev)
 {
@@ -169,10 +149,10 @@ static int i2c_mux_reg_probe(struct platform_device *pdev)
 		memcpy(&mux->data, dev_get_platdata(&pdev->dev),
 			sizeof(mux->data));
 	} else {
-		ret = i2c_mux_reg_probe_dt(mux, pdev);
+		ret = i2c_mux_reg_probe_fw(mux, &pdev->dev);
 		if (ret < 0)
 			return dev_err_probe(&pdev->dev, ret,
-					     "Error parsing device tree");
+					     "Error parsing firmware description\n");
 	}
 
 	parent = i2c_get_adapter(mux->data.parent);
@@ -180,8 +160,6 @@ static int i2c_mux_reg_probe(struct platform_device *pdev)
 		return -EPROBE_DEFER;
 
 	if (!mux->data.reg) {
-		dev_info(&pdev->dev,
-			"Register not set, using platform resource\n");
 		mux->data.reg = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
 		if (IS_ERR(mux->data.reg)) {
 			ret = PTR_ERR(mux->data.reg);

---
base-commit: 0031c06807cfa8aa51a759ff8aa09e1aa48149af
change-id: 20260305-i2c-mux-reg-552203da8564

Best regards,
--  
Abdurrahman Hussain <abdurrahman@nexthop.ai>