mismatch between FACP and chipset spec

Andriy Gapon avg at icyb.net.ua
Sun Apr 6 12:11:22 UTC 2008

on 28/02/2008 21:29 Andriy Gapon said the following:
> on 28/02/2008 20:17 Nate Lawson said the following:
>> Andriy Gapon wrote:
>>> But addresses given for PM1a_CNT_BLK are not documented at all! On the
>>> other hand ACPI description of that register perfectly matches
>>> description of PIIX4 PMCNTRL register that is located at 0x4004 with a
>>> given base address. So, this is 0x4040 vs. 0x4004, looks like a possible
>>> typo/mistake by an author of ACPI tables for this motherboard.
>> 440BX is pretty old, and typos like that were common back then.  ACPI 
>> was less used and drivers would just hardcode 0x4004 or whatever.
>>> Question: is there any way I can way override the address of
>>> PM1a_CNT_BLK? My guess is that there is zero chance that there would be
>>> any BIOS updates for this old and exotic motherboard (MP2-BX-X).
>> No generic way.  You'd have to add a quirk to acpi.c/acpi_quirks and use 
>> that to override FADT.
>>> I think that this register is mostly useful for BM_RLD bit which is used
>>> in C3 support. I don't use C3 (there is an errata for C3 with this
>>> chipset and there is no PM2_CNT register defined anyway), but I am
>>> curios anyway.
>> Seems like a lot of effort for no gain.  Since you are getting good at 
>> debugging, can we get you newer hardware to play with?  :)
> Nate,
> thank you for pointing me to acpi_quirks and for confirming my doubts
> over worthwhileness of this endeavor.

I knew that I wouldn't be able to keep my hands off it :-)
Actually that PM1a_CNT_BLK typo caused one very minor annoyance for me
(but still an annoyance!) - 'shutdown -p' would cause the machine to
hang right after 'Powering system off using ACPI' line.
It seems that ACPI power off requires a write to PM1a_CNT_BLK area and
the hardware doesn't tolerate a write to a bogus IO register.
Attached is small patch that fixes the issue for my particular system.
It is a bit ugly but I couldn't think of another way for a quirk like this.

Andriy Gapon
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