@@ -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;
}