https://bugzilla.kernel.org/show_bug.cgi?id=112971
Bug ID: 112971
Summary: Make ACPI BIOS warning more accurate
Product: ACPI
Version: 2.5
Kernel Version: 4.4.1-2-ARCH
Hardware: All
OS: Linux
Tree: Mainline
Status: NEW
Severity: enhancement
Priority: P1
Component: ACPICA-Core
Assignee: [email protected]
Reporter: [email protected]
Regression: No
Created attachment 204441
--> https://bugzilla.kernel.org/attachment.cgi?id=204441&action=edit
cat /sys/firmware/acpi/tables/FACP | Use iasl -d FACP.aml to decompile
ACPI BIOS Warning (bug): Optional FADT field Pm2ControlBlock has zero address
or length: 0x0000000000000000/0x1 (20150930/tbfadt-654)
This is what I was getting in dmesg at every boot, so I stared to look at my
ACPI tables and documentation for clues.
Thankfully iasl pointed me out to the right one (attached).
Basically PM2 Control Block Length is set to 1 (so kernel thinks PM2 register
block is supported) but PM2_CNT_BLK address is 0 (as in the unsupported case).
http://www.uefi.org/sites/default/files/resources/ACPI_6_1.pdf#169
After making up this rationale though, I felt like the warning message
(http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/acpi/acpica/tbfadt.c#n658)
was.. kind of misleading
The problem is not really with "[something] optional that is 0".
It's more about "something optional (advertised as supported!) that is 0".
And I thought the wording could be improved.
Also, somewhat unrelated..
I guess this "mismatch" is completely harmless, and even though it's just about
setting a single bit to 0, it's not even worth that hassle.
But I was wondering: could there ever be any *really* FADT problematic
scenario?
I mean.. so much that something like CONFIG_ACPI_CUSTOM_DSDT would make sense?
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