ichwd: add support for TCO watchdog timer in Lewisburg PCH (C620)
The change is based on public documents listed below as well as Linux
changes and the code developed by Kostik.
The documents:
- Intel® C620 Series Chipset Platform Controller Hub Datasheet
- Intel® 100 Series and Intel® C230 Series Chipset Family Platform Controller Hub (PCH) Datasheet - Volume 2 of 2
Interesting Linux commits:
- https://github.com/torvalds/linux/commit/9424693035a57961a8eb09e96aab315a7096535d
- https://github.com/torvalds/linux/commit/2a7a0e9bf7b32e838d873226808ab8a6c00148f7
The peculiarity of the new chipsets is that the watchdog resources are
configured in PCI registers of SMBus controller and Power Management
function as opposed to the LPC bridge. I took a simplistic approach of
querying the resources from the respective PCI devices. ichwd is still
a device on isa bus. The PCI devices are found by their slot and
function defined in the datasheets as siblings of the upstream LPC
bridge.
There are some shortcuts and missing features.
First of all, I have not implemented the functionality required to clear
the no-reboot bit. That would require writing to a special PCI
configuration register of a hidden / invisible PCI device after which
the device would start responding to accesses to other registers. The
no-reboot bit was not set on my test hardware, so I decided to leave its
handling for the later time.
Also, I did not try to handle the case where the watchdog resources are
not configured by the hardware as well as the case where ACPI defined
operational region conflicts with the watchdog resources. My test
system did not have either of those problem, so, again, I decided to
leave those cases until later.
See this Linux commit for some details of the ACPI problem:
https://github.com/torvalds/linux/commit/a7ae81952cdab56a1277bd2f9ed7284c0f575120
Finally, I have added only the PCI ID found on my test system. I think
that more IDs can be added as the change gets tested.
Tested on Dell PowerEdge R740.
PR: 222079
Reviewed by: mav, kib
MFC after: 3 weeks
Relnotes: maybe
Sponsored by: Panzura
Differential Revision: https://reviews.freebsd.org/D17585