Recently we met a touchscreen problem on some Thinkpad machines, the touchscreen driver (i2c-hid) is not loaded and the touchscreen can't work.
An i2c ACPI device with the name WACF2200 is defined in the BIOS, with the current rule in matching_id(), this device will be regarded as a PNP device since there is WACFXXX in the acpi_pnp_device_ids[] and this PNP device is attached to the acpi device as the 1st physical_node, this will make the i2c bus match fail when i2c bus calls acpi_companion_match() to match the acpi_id_table in the i2c-hid driver.
WACF2200 is an i2c device instead of a PNP device, after adding the string length comparing, the matching_id() will return false when matching WACF2200 and WACFXXX, and it is reasonable to compare the string lenth when matching two ids.
Cc: stable@vger.kernel.org Signed-off-by: Hui Wang hui.wang@canonical.com --- drivers/acpi/acpi_pnp.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/drivers/acpi/acpi_pnp.c b/drivers/acpi/acpi_pnp.c index 4ed755a963aa..8f2dc176bb41 100644 --- a/drivers/acpi/acpi_pnp.c +++ b/drivers/acpi/acpi_pnp.c @@ -319,6 +319,9 @@ static bool matching_id(const char *idstr, const char *list_id) { int i;
+ if (strlen(idstr) != strlen(list_id)) + return false; + if (memcmp(idstr, list_id, 3)) return false;