1 files changed, 37 insertions, 4 deletions

diff --git a/drivers/i2c/i2c-core-acpi.c b/drivers/i2c/i2c-core-acpi.c
index d6037a328669..d2499f302b50 100644
--- a/drivers/i2c/i2c-core-acpi.c
+++ b/drivers/i2c/i2c-core-acpi.c
@@ -355,6 +355,25 @@ static const struct acpi_device_id i2c_acpi_force_400khz_device_ids[] = {
 	{}
 };
 
+static const struct acpi_device_id i2c_acpi_force_100khz_device_ids[] = {
+	/*
+	 * When a 400KHz freq is used on this model of ELAN touchpad in Linux,
+	 * excessive smoothing (similar to when the touchpad's firmware detects
+	 * a noisy signal) is sometimes applied. As some devices' (e.g, Lenovo
+	 * V15 G4) ACPI tables specify a 400KHz frequency for this device and
+	 * some I2C busses (e.g, Designware I2C) default to a 400KHz freq,
+	 * force the speed to 100KHz as a workaround.
+	 *
+	 * For future investigation: This problem may be related to the default
+	 * HCNT/LCNT values given by some busses' drivers, because they are not
+	 * specified in the aforementioned devices' ACPI tables, and because
+	 * the device works without issues on Windows at what is expected to be
+	 * a 400KHz frequency. The root cause of the issue is not known.
+	 */
+	{ "ELAN06FA", 0 },
+	{}
+};
+
 static acpi_status i2c_acpi_lookup_speed(acpi_handle handle, u32 level,
 					   void *data, void **return_value)
 {
@@ -373,6 +392,9 @@ static acpi_status i2c_acpi_lookup_speed(acpi_handle handle, u32 level,
 	if (acpi_match_device_ids(adev, i2c_acpi_force_400khz_device_ids) == 0)
 		lookup->force_speed = I2C_MAX_FAST_MODE_FREQ;
 
+	if (acpi_match_device_ids(adev, i2c_acpi_force_100khz_device_ids) == 0)
+		lookup->force_speed = I2C_MAX_STANDARD_MODE_FREQ;
+
 	return AE_OK;
 }
 
@@ -445,6 +467,11 @@ static struct i2c_client *i2c_acpi_find_client_by_adev(struct acpi_device *adev)
 	return i2c_find_device_by_fwnode(acpi_fwnode_handle(adev));
 }
 
+static struct i2c_adapter *i2c_acpi_find_adapter_by_adev(struct acpi_device *adev)
+{
+	return i2c_find_adapter_by_fwnode(acpi_fwnode_handle(adev));
+}
+
 static int i2c_acpi_notify(struct notifier_block *nb, unsigned long value,
 			   void *arg)
 {
@@ -471,11 +498,17 @@ static int i2c_acpi_notify(struct notifier_block *nb, unsigned long value,
 			break;
 
 		client = i2c_acpi_find_client_by_adev(adev);
-		if (!client)
-			break;
+		if (client) {
+			i2c_unregister_device(client);
+			put_device(&client->dev);
+		}
+
+		adapter = i2c_acpi_find_adapter_by_adev(adev);
+		if (adapter) {
+			acpi_unbind_one(&adapter->dev);
+			put_device(&adapter->dev);
+		}
 
-		i2c_unregister_device(client);
-		put_device(&client->dev);
 		break;
 	}