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

[Paul Menzel (Code Review)]

Attention is currently required from: Subrata Banik, Maulik V Vaghela, Sridhar Siricilla, Nick Vaccaro, Eric Lai, Felix Held.
Paul Menzel 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 4:

(8 comments)

Commit Message:

https://review.coreboot.org/c/coreboot/+/63552/comment/bc7f1abc_63c361d6 
PS4, Line 9: calls into
Just “calls”?

https://review.coreboot.org/c/coreboot/+/63552/comment/4307c95e_4d5e2e4d 
PS4, Line 12: Without this patch the PMC IPC timeout issue is seen
Currently, the PMC IPC times out while sending the USB-C (0xA7) command during …

https://review.coreboot.org/c/coreboot/+/63552/comment/6d57a7de_0dd91c14 
PS4, Line 12: the PMC IPC timeout issue
As you use “the”, is it a common known problem? Is there some errata?

https://review.coreboot.org/c/coreboot/+/63552/comment/176a13d4_34313430 
PS4, Line 34: active USB port
Excuse my ignorance, does “active” mean, something needs to be connected to the port?

https://review.coreboot.org/c/coreboot/+/63552/comment/6a0ed398_4614430d 
PS4, Line 37: SMI handler
Why does this have to be done in SMM?

https://review.coreboot.org/c/coreboot/+/63552/comment/8bdaf478_65e3a727 
PS4, Line 9: This patch calls into `xhci_host_reset()` function to perform XHCI
           : controller reset.
           : 
           : Without this patch the PMC IPC timeout issue is seen while sending the
           : USB-C (0xA7) command during poweron from S5 (S5->S4->S3->S0).
           : 
           : On Brya variants, poweron from S5 state results in PMC error while
           : sending PMC IPC (0xA7) to USB-C active ports, log here:
           : 
           : localhost ~ # cbmem -c | grep ERROR
           : 
           : [ERROR]  PMC IPC timeout after 1000 ms
           : [ERROR]  PMC IPC command 0x200a7 failed
           : [ERROR]  pmc_send_ipc_cmd failed
           : [ERROR]  Failed to setup port:0 to initial state
           : [ERROR]  PMC IPC timeout after 1000 ms
           : [ERROR]  PMC IPC command 0x200a7 failed
           : [ERROR]  pmc_send_ipc_cmd failed
           : [ERROR]  Failed to setup port:1 to initial state
           : [ERROR]  PMC IPC timeout after 1000 ms
           : [ERROR]  PMC IPC command 0x20a0 failed
           : 
           : This problem is not seen while powering on from G3 (G3->S5->S4->S3->S0).
           : 
           : During poweron the state of USB ports are not the same between S5 and G3
           : and it appears that the active USB port still is in U3 (suspend) while
           : PMC tries to send the IPC command, which results in a timeout.
           : 
           : This patch utilises the S5 SMI handler to reset the XHCI controller
           : using `xhci_host_reset()` prior entering into the S5, it helps to
           : restore the port state to active hence, no PMC timeout is seen with
           : this code change.
I’d start by stating the problem, and then describing the fix.

https://review.coreboot.org/c/coreboot/+/63552/comment/4bcba6de_f595e60d 
PS4, Line 41: 
Does resetting add anything to the shutdown time? (Boottime should be unaffected?)

File src/mainboard/google/brya/smihandler.c:

https://review.coreboot.org/c/coreboot/+/63552/comment/9e86deb0_8c2b7e7e 
PS4, Line 15: 	/* USB sleep preparations */
Maybe elaborate?