Change in coreboot[master]: mb/google/brya: Reset XHCI controller while preparing for S5

[Nico Huber (Code Review)]

Attention is currently required from: Maulik V Vaghela, Paul Menzel, Sridhar Siricilla, Arthur Heymans, Nick Vaccaro, Eric Lai, Felix Held.
Nico Huber has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/63552 )

Change subject: mb/google/brya: Reset XHCI controller while preparing for S5
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Patch Set 6:

(1 comment)

Commit Message:

https://review.coreboot.org/c/coreboot/+/63552/comment/5ad9a7ad_b4b9c9bb 
PS4, Line 37: SMI handler
> > Sorry, thinking error on my part. coreboot of course does not run anymore during shutdown (besides the installed handlers).
> >
> > But, why can’t this be worked around/fixed in the OS driver?
>
> fixing in FW is comparatively easier 😊

How so? You had to add a whole new API function (and should have added
a new file for it, AFAICS; also, you use PCH_DEV_XHCI which contains a
workaround for NULL pointers which should be fixed). In Linux, OTOH,
you probably just need to set a correct quirk flag.

Doing it in SMM makes OS developers expect that they don't have to
handle it, even provides them an excuse not to do it, and that weakens
the ecosystem. IIRC, SMI handlers were originally added to coreboot
because of a similar story. Now we risk to repeat the 10y+ old mistake.