From 3107a9a3241d6b585cbc08c7035b03fa44e9fb94 Mon Sep 17 00:00:00 2001 From: Mario Limonciello Date: Tue, 8 Sep 2026 14:34:58 -0500 Subject: [PATCH] ACPI: utils: Ignore leading root scope prefix in string _UID match Firmware may express an ACPI namespace path used as a _UID with or without the leading root scope character ('\'). For example, an AMD IVRS IVHD ACPI HID device entry may carry a character UID of "\_SB.MHSP" while the corresponding device's _UID evaluates to "_SB.MHSP" (or vice versa). This semantic difference is due to how Windows PnP enumerates and uses devices. acpi_str_uid_match() compared the two strings verbatim, so such entries failed to match on the UID even though they refer to the same object. In the AMD IOMMU case (get_acpihid_device_id()) this caused the exact HID+UID match to be missed and the code to fall through to the HID-only path, spuriously raising a FW_BUG. Skip a single leading '\' on either string before comparing so that paths that differ only by the root scope prefix are treated as a match. The integer _UID path is unaffected. [ rjw: It is sad that making this change needed to be considered at all. That being said, it is also rather unlikely that someone will use a leading backslash as the only difference to distinguish one UID string from antother, so this change is unlikely to break anything. ] Signed-off-by: Mario Limonciello [ rjw: Added separator line to a kerneldoc comment ] [ rjw: Droppend Link: tag with a limited access target ] Signed-off-by: Rafael J. Wysocki --- include/acpi/acpi_bus.h | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h index a10a591c18b2..22be27e02682 100644 --- a/include/acpi/acpi_bus.h +++ b/include/acpi/acpi_bus.h @@ -830,7 +830,15 @@ static inline bool acpi_str_uid_match(struct acpi_device *adev, const char *uid2 { const char *uid1 = acpi_device_uid(adev); - return uid1 && uid2 && !strcmp(uid1, uid2); + if (!uid1 || !uid2) + return false; + + if (*uid1 == '\\' && uid1[1]) + uid1++; + if (*uid2 == '\\' && uid2[1]) + uid2++; + + return !strcmp(uid1, uid2); } static inline bool acpi_int_uid_match(struct acpi_device *adev, u64 uid2) @@ -857,6 +865,10 @@ static inline bool acpi_int_uid_match(struct acpi_device *adev, u64 uid2) * * Matches UID in @adev with given @uid2. * + * If both the UID in @adev and @uid2 are strings, they are compared + * after optionally skipping a leading backslash ('\') if the given + * string contains additional characters. + * * Returns: %true if matches, %false otherwise. */ #define acpi_dev_uid_match(adev, uid2) \