https://bugzilla.kernel.org/show_bug.cgi?id=15701
Summary: Linux should ignore Producer/Consumer bit in _CRS
Address Space descriptors
Product: ACPI
Version: 2.5
Kernel Version: 2.6.34-rc3
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: Config-Other
AssignedTo: [email protected]
ReportedBy: [email protected]
Regression: No
In the ACPI PCI host bridge driver, the arch-specific code parses _CRS
resources to learn the windows forwarded to the PCI bus. Both ia64 and x86
follow section 6.4.3.5 of ACPI spec 4.0, which says that Bit[0] of Byte 4 in
QWord, DWord, Word, and Extended Address Space Descriptors is a
"Consumer/Producer" bit. This bit is set if the device consumes the resource,
and clear if the device produces and consumes it, i.e., if the device forwards
the resource to a downstream bus.
However, it is rumored that BIOSes have not used the Consumer/Producer bit
consistently, and the bit was documented as "Ignored" in ACPI 2.0c. The bit
was added back in 3.0, but this apparently was a mistake.
I experimented with Windows Server 2008 R2 in a qemu environment, running
SeaBIOS, where I could modify the _CRS description and see how Windows handled
it.
The PCI host bridge windows should be described as ResourceProducer, and the
HPET registers should be described as ResourceConsumer. As shown here, I
modified the SeaBIOS DSDT to reverse both flags, so the bridge window is a
Consumer and the HPET registers are a Producer:
Device(PCI0) {
Name (_HID, EisaId ("PNP0A03"))
Name (_CRS, ResourceTemplate ()
{
...
DWordMemory (ResourceConsumer, PosDecode, MinFixed, MaxFixed,
NonCacheable, ReadWrite,
0x00000000, // Address Space Granularity
0xE0000000, // Address Range Minimum
0xFEBFFFFF, // Address Range Maximum
0x00000000, // Address Translation Offset
0x1EC00000, // Address Length
,, , AddressRangeMemory, TypeStatic)
})
}
Device(HPET) {
Name(_HID, EISAID("PNP0103"))
Name(_CRS, ResourceTemplate() {
DWordMemory(
ResourceProducer, PosDecode, MinFixed, MaxFixed,
NonCacheable, ReadWrite,
0x00000000,
0xFED00000,
0xFED003FF,
0x00000000,
0x00000400 /* 1K memory: FED00000 - FED003FF */
)
})
}
The attachments of Windows Device Manager screenshots show that Windows
interpreted the bridge ResourceConsumer as a window and the HPET
ResourceProducer as normal registers. PCI devices, e.g., the NIC and VGA,
inside the ResourceConsumer range worked normally.
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