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 <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>

0 files changed, 0 insertions, 0 deletions