[coreboot] Discussion about fixing dead code / ACPI TRAP

[Patrick Rudolph]

Hello community,
I'll want to start a discussion about fixing dead code.

How it all started:
I tried to run docking code on Lenovo T400 and found it's not working.
While investigation it turns out that the ACPI TRAP mechanism is being
used, and that it doesn't start the SMM handler.
The mechanism works fine on Lenovo X60 and T60 because they enable the
IO TRAP in romstage.

Fixing it:
I found that every Intel southbridge has code to support ACPI TRAP, but
doesn't enable the trap mechanism by default. The idea is to enable ACPI
TRAP in southbridge depending on a Kconfig option. The fix is here [1]

The problem:
Nico pointed out that while the fix might be technically correct, it
would touch a lot dead code. There are only a very few boards using the
mechanism.

The following questions came up:
Should dead code be "fixed" at all ?
Should the "dead" code be removed on platforms that do not use ACPI TRAP
? Developers that want to use the mechanism in the future will have to
reimplement it.
As it touches a lot "dead" code, it cannot be easily tested on some
platforms. Should patches be accepted for those platforms ?
Should we get rid of ACPI TRAP mechanism and reimplement everything in
AML only ?
Should we mark ACPI TRAP as bad and force future development to use AML
only ?

Regards,
Patrick

References:
[1]: https://review.coreboot.org/#/c/20328/