acpi timer reads all ones [Was: efirtc + atrtc at the same time]

[Andriy Gapon]

On 27/05/2020 11:13, Andriy Gapon wrote:
> I added more diagnostics and it seems to support the idea that the problem is
> related to I/O cycles and bridges.
> 
> ACPI timer suddenly starts returning 0xffffffff and that lasts for tens of
> microseconds before the timer goes back to returning normal values with an
> expected increase.
> AMD provides a proprietary way to access ACPI registers via MMIO (0xfed808xx).
> That mechanism is unaffected, ACPI timer register always returns good values.
> 
> The problem seems to happen when restoring configuration of a particular PCI
> bridge.  What's interesting is that the bridge decodes one memory range and one
> I/O range.
> 
> Looking at pci_cfg_restore() I wonder if it is wise to restore PCIR_COMMAND so
> early.  Could it be that after the resume the bridge is configured with a wrong
> I/O range (e.g., too wide) and by writing PCIR_COMMAND we enable that decoding.
>  So, the bridge steals I/O cycles destined for ACPI support hardware.  If there
> is nothing behind the bridge to handle those ports, then we get those bad readings.
> Once the bridge configuration is fully restored, the I/O handling goes back to
> normal.

>From what I see, this looks like a BIOS bug.
Upon resume, it swaps window configurations of pcib1 and pcib2 (until FreeBSD
restores them).  pcib1 originally does not have an I/O window.  So, BIOS
programs both base and limit of pcib2 I/O window to zero.   When FreeBSD writes
its command register to enable I/O decoding it starts claiming 0x0 - 0xFFF I/O
port range.  That covers the ACPI ports at 0x8xx.

Some printf-s.
>From (verbose) boot time:
pcib1:   domain            0
pcib1:   secondary bus     1
pcib1:   subordinate bus   1
pcib1:   memory decode     0xfea00000-0xfeafffff
pcib2:   domain            0
pcib2:   secondary bus     2
pcib2:   subordinate bus   2
pcib2:   I/O decode        0xf000-0xffff
pcib2:   memory decode     0xfe900000-0xfe9fffff

My printf-s from resume time:
pcib1: old I/O base (low): 0xf1
pcib1: old I/O base (high): 0x0
pcib1: old I/O limit (low): 0x1
pcib1: old I/O limit (high): 0x0
pcib2: old I/O base (low): 0x1
pcib2: old I/O base (high): 0x0
pcib2: old I/O limit (low): 0x1
pcib2: old I/O limit (high): 0x0

-- 
Andriy Gapon