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ACPI: utils: Ignore leading root scope prefix in string _UID match

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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 <mario.limonciello@amd.com>
[ rjw: Added separator line to a kerneldoc comment ]
[ rjw: Droppend Link: tag with a limited access target ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Mario Limonciello 2026-09-08 14:34:58 -05:00 committed by Rafael J. Wysocki
parent 78ddbfaa72
commit 3107a9a324
1 changed files with 13 additions and 1 deletions
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14
include/acpi/acpi_bus.h
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@ -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) \