The ACPI specification (ACPI 5.0A, Section 6.3.7) says:
_STA may return bit 0 clear (not present) with bit 3 set (device is
functional). This case is used to indicate a valid device for which
no device driver should be loaded (for example, a bridge device.)
Children of this device may be present and valid. OSPM should
continue enumeration below a device whose _STA returns this bit
combination.
Evidently, some BIOSes follow that and return 0x0A from _STA, which
causes problems to happen when they trigger bus check or device check
notifications for those devices too. Namely, ACPIPHP thinks that they
are gone and may drop them, for example, if such a notification is
triggered during a resume from system suspend.
To fix that, modify ACPICA to regard devies as present and
functioning if _STA returns both the ACPI_STA_DEVICE_ENABLED
and ACPI_STA_DEVICE_FUNCTIONING bits set for them.
Reported-and-tested-by: Peter Wu <lekensteyn@gmail.com>
Cc: 3.12+ <stable@vger.kernel.org> # 3.12+
[rjw: Subject and changelog, minor code modifications]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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