[PATCH 1/2] i2c: acpi: skip generic I2C device when vendor-specific sibling exists

[Edward Blair <edward.blair@gmail.com>]

Some BIOS implementations (notably ASUS Z690/Z790/X670E motherboards)
declare both a generic UCSI device (MSFT8000) and a vendor-specific
device (e.g., ITE8853) as ACPI children of the same I2C controller,
both referencing the same I2C slave address.

During ACPI I2C enumeration, whichever device is walked first claims
the address, causing the second to fail with -EBUSY. When the generic
MSFT8000 device registers first, the vendor-specific driver cannot
bind, losing access to device-specific features like GPIO interrupt
resources that are only declared on the vendor-specific ACPI device.

Fix this by checking, before registering a known generic I2C device,
whether a sibling ACPI device exists at the same address on the same
adapter. If so, skip the generic device to let the vendor-specific
one register instead.

Signed-off-by: Edward Blair <edward.blair@gmail.com>
---
 drivers/i2c/i2c-core-acpi.c | 88 +++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)

diff --git a/drivers/i2c/i2c-core-acpi.c b/drivers/i2c/i2c-core-acpi.c
index 2cbd31f77..87582eac7 100644
--- a/drivers/i2c/i2c-core-acpi.c
+++ b/drivers/i2c/i2c-core-acpi.c
@@ -137,6 +137,17 @@ static const struct acpi_device_id i2c_acpi_ignored_device_ids[] = {
 	{}
 };
 
+/*
+ * Generic I2C device IDs that may be duplicated by vendor-specific devices.
+ * When a vendor-specific sibling exists at the same address, the generic
+ * device is skipped to avoid -EBUSY address conflicts.
+ */
+static const struct acpi_device_id i2c_acpi_generic_device_ids[] = {
+	/* Microsoft UCSI - often paired with vendor-specific UCSI device */
+	{ "MSFT8000" },
+	{}
+};
+
 struct i2c_acpi_irq_context {
 	int irq;
 	bool wake_capable;
@@ -274,6 +285,76 @@ static int i2c_acpi_get_info(struct acpi_device *adev,
 	return 0;
 }
 
+struct i2c_acpi_sibling_check {
+	struct acpi_device *self;
+	struct i2c_adapter *adapter;
+	unsigned short addr;
+	bool found;
+};
+
+static int i2c_acpi_check_sibling_addr(struct acpi_device *adev, void *data)
+{
+	struct i2c_acpi_sibling_check *check = data;
+	struct i2c_acpi_lookup lookup;
+	struct i2c_board_info info;
+
+	if (adev == check->self)
+		return 0;
+
+	/* Only yield to vendor-specific devices, not other generic ones */
+	if (!acpi_match_device_ids(adev, i2c_acpi_generic_device_ids))
+		return 0;
+
+	memset(&lookup, 0, sizeof(lookup));
+	lookup.info = &info;
+	lookup.index = -1;
+
+	if (i2c_acpi_do_lookup(adev, &lookup))
+		return 0;
+
+	if (!device_match_acpi_handle(&check->adapter->dev,
+				      lookup.adapter_handle))
+		return 0;
+
+	if (info.addr == check->addr) {
+		check->found = true;
+		return 1;
+	}
+
+	return 0;
+}
+
+/*
+ * Check whether this generic ACPI device has a vendor-specific sibling at the
+ * same I2C address. Some BIOS implementations (e.g., ASUS Z690/Z790/X670E)
+ * declare both a generic UCSI device (MSFT8000) and a vendor-specific device
+ * (e.g., ITE8853) at the same address. Skip the generic one so the vendor
+ * driver can bind with proper interrupt and device-specific resources.
+ */
+static bool i2c_acpi_has_vendor_sibling(struct acpi_device *adev,
+					struct i2c_adapter *adapter,
+					struct i2c_board_info *info)
+{
+	struct acpi_device *parent;
+	struct i2c_acpi_sibling_check check;
+
+	if (acpi_match_device_ids(adev, i2c_acpi_generic_device_ids))
+		return false;
+
+	parent = acpi_dev_parent(adev);
+	if (!parent)
+		return false;
+
+	check.self = adev;
+	check.adapter = adapter;
+	check.addr = info->addr;
+	check.found = false;
+
+	acpi_dev_for_each_child(parent, i2c_acpi_check_sibling_addr, &check);
+
+	return check.found;
+}
+
 static void i2c_acpi_register_device(struct i2c_adapter *adapter,
 				     struct acpi_device *adev,
 				     struct i2c_board_info *info)
@@ -302,6 +383,13 @@ static acpi_status i2c_acpi_add_device(acpi_handle handle, u32 level,
 	if (!adev || i2c_acpi_get_info(adev, &info, adapter, NULL))
 		return AE_OK;
 
+	if (i2c_acpi_has_vendor_sibling(adev, adapter, &info)) {
+		dev_info(&adapter->dev,
+			 "skipping %s in favor of vendor-specific device at 0x%02x\n",
+			 dev_name(&adev->dev), info.addr);
+		return AE_OK;
+	}
+
 	i2c_acpi_register_device(adapter, adev, &info);
 
 	return AE_OK;
-- 
2.53.0