From b08221c40febcbda9309dd70c61cf1b0ebb0e351 Mon Sep 17 00:00:00 2001
From: Hui Wang <hui.wang@canonical.com>
Date: Fri, 11 Dec 2020 10:18:14 +0800
Subject: [PATCH] ACPI: PNP: compare the string length in the matching_id()
Git-commit: b08221c40febcbda9309dd70c61cf1b0ebb0e351
Patch-mainline: v5.11-rc1
References: git-fixes

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>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 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;
 
-- 
2.26.2