[PATCH 4.14 187/242] ACPI: PNP: compare the string length in the matching_id()

Greg Kroah-Hartman
2020-12-28T16:18:04Z

From: Hui Wang <hui.wang@canonical.com>

commit b08221c40febcbda9309dd70c61cf1b0ebb0e351 upstream.

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 length when matching two IDs.

Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Hui Wang <hui.wang@canonical.com>
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/acpi/acpi_pnp.c | 3 +++
1 file changed, 3 insertions(+)

--- a/drivers/acpi/acpi_pnp.c
+++ b/drivers/acpi/acpi_pnp.c
@@ -320,6 +320,9 @@ static bool matching_id(const char *idst
{
int i;

+ if (strlen(idstr) != strlen(list_id))
+ return false;
+
if (memcmp(idstr, list_id, 3))
return false;