On Fri, 20 Jun 2008, Matthew Garrett wrote:
> > Ah, indeed, thanks for the hint. This is the output of
>
> Right. My recollection of this is somewhat hazy, so here's something I
> wrote a couple of years ago:
>
> "If you dig through the DSDT code for the 6125, you'll find a bit where
> it writes 0x14 to 0xfec00000 and then checks whether offset 0x12 from
> there is 1. In other words, it's checking if pin 2 of the io-apic is
> masked. If it's not masked (that is, offset 0x12 is 0 and irq 2 is
> enabled) it sets another bit in a register. This is then checked by the
> thermal zone code which as a result sets the thermal trip temperatures
> to 16 degrees Celsius. This bites when the acpi_skip_timer_override
> option is used in Linux."
>
> I have no idea what this code is for, but it's pretty clear that Windows
> sets it up in such a way that this isn't true.
Thanks, that is a very useful insight indeed. I went through the effort
to locate a DSDT dump for the nx6325. Here are the relevant parts, first
the definition:
OperationRegion (C253, SystemMemory, 0xFEC00000, 0x14)
Field (C253, ByteAcc, NoLock, Preserve)
{
C08B, 8,
Offset (0x10),
Offset (0x12),
C08C, 1
}
So now we have got a block defined, which corresponds to the location of
the I/O APIC and is 0x14 bytes long. That is not top quality code, I
would say, but surely it achieves what it is meant to. Within that block
two fields are defined:
1. An 8-bit one at the byte offset 0 -- that corresponds to the index
register.
2. A 1-bit one at the byte offset 0x12 -- that corresponds to the bit #16
of the data register, which for redirection entries is the mask
register.
And then we have a method elsewhere, which uses the above definition:
Method (_INI, 0, NotSerialized)
{
C084 ()
Store (0x00, \_SB.C074.C089.C08A)
Store (0x14, C08B)
If (LEqual (C08C, 0x00))
{
Store (0x01, \_SB.C074.C089.C08A)
}
}
_SB.C074.C089.C08A refers to a piece of 8-bit data at an offset of 0xf0
accessed through an index and data registers located at 0x72 and 0x73 in
the port I/O space. That's probably an extended part of the NVRAM
associated with the RTC.
That location is referred from two places as follows:
If (LEqual (\_SB.C074.C089.C08A, 0x01))
{
Store (0x0B4B, Local2)
}
which is obviously that 16C trip point mentioned, overriding the result
of the method obtained from the respective device in the usual way, and:
If (LEqual (\_SB.C074.C089.C08A, 0x00))
{
\_SB.C074.C0E3.C149.C195 (0x00)
}
elsewhere which sets a location in the embedded controller which seems
related to battery control. Overall my guts feeling is it's some
debugging or leftover code meant for a different configuration.
This is further confirmed by another block defined next to the one quoted
above:
OperationRegion (C254, SystemIO, 0x21, 0x01)
Field (C254, ByteAcc, NoLock, Preserve)
{
C255, 1
}
which quite similarly defines a mask for the 8254 timer interrupt in the
master 8259A. This is nowhere used though -- any references may have been
removed with the I/O APIC part not adjusted accordingly. Note that the
I/O APIC mask defined above is not quite a mask for the 8254 timer
interrupt in this system (as it is the ExtINTA 8259A cascade), but it is a
common location for one.
Anyway, it's clear it's firmware that is at fault here and not hardware.
There are actually two bugs -- first is described above and the other one
is the IRQ0 override, which is clearly incorrect. The piece of hardware
comes from a reputable vendor, so it should be possible to submit a bug
report for the firmware. Anybody happens to know the appropriate contact?
Meanwhile we may consider implementing a workaround. I think one that
does not hurt competent vendors would be preferable. The DSDT containing
the rubbish described here is marked with an OEM ID: "HP " and OEM
Table ID: "SB400". These keys could be used to remove IRQ0 information
from the IRQ tables. Our code is prepared to handle such a case.
Something easy to do for a seasoned ACPI fiddler, I suppose. ;)
Windows does not trigger this bug, because it stays away from the 8254 on
APIC platforms and uses the RTC for the timer instead I am told.
Maciej
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