ACPI: EC: Relax sanity check of the ECDT ID string

JIRA: https://issues.redhat.com/browse/RHEL-114092

commit 963e22c
Author: Armin Wolf <W_Armin@gmx.de>
Date: Tue, 12 Aug 2025 19:16:27 +0000

It turns out that the ECDT table inside the ThinkBook 14 G7 IML
contains a valid EC description but an invalid ID string
("_SB.PC00.LPCB.EC0"). Ignoring this ECDT based on the invalid
ID string prevents the kernel from detecting the built-in touchpad,
so relax the sanity check of the ID string and only reject ECDTs
with empty ID strings.

Reported-by: Ilya K <me@0upti.me>
Fixes: 7a0d59f ("ACPI: EC: Ignore ECDT tables with an invalid ID string")
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Tested-by: Ilya K <me@0upti.me>
Link: https://patch.msgid.link/20250729062038.303734-1-W_Armin@gmx.de
Cc: 6.16+ <stable@vger.kernel.org> # 6.16+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Mark Langsdorf <mlangsdo@redhat.com>

Author: mlangsdorf

drivers/acpi/ec.c

@@ -2033,7 +2033,7 @@ void __init acpi_ec_ecdt_probe(void)
 		goto out;
 	}
 
-	if (!strstarts(ecdt_ptr->id, "\\")) {
+	if (!strlen(ecdt_ptr->id)) {
 		/*
 		 * The ECDT table on some MSI notebooks contains invalid data, together
 		 * with an empty ID string ("").
@@ -2042,9 +2042,13 @@ void __init acpi_ec_ecdt_probe(void)
 		 * a "fully qualified reference to the (...) embedded controller device",
 		 * so this string always has to start with a backslash.
 		 *
-		 * By verifying this we can avoid such faulty ECDT tables in a safe way.
+		 * However some ThinkBook machines have a ECDT table with a valid EC
+		 * description but an invalid ID string ("_SB.PC00.LPCB.EC0").
+		 *
+		 * Because of this we only check if the ID string is empty in order to
+		 * avoid the obvious cases.
 		 */
-		pr_err(FW_BUG "Ignoring ECDT due to invalid ID string \"%s\"\n", ecdt_ptr->id);
+		pr_err(FW_BUG "Ignoring ECDT due to empty ID string\n");
 		goto out;
 	}