Duncan Laurie has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/43831 )
Change subject: soc/intel/tigerlake: Set default USB3 de-emphasis to -3.5dB ......................................................................
Patch Set 1:
(1 comment)
https://review.coreboot.org/c/coreboot/+/43831/1//COMMIT_MSG Commit Message:
https://review.coreboot.org/c/coreboot/+/43831/1//COMMIT_MSG@10 PS1, Line 10: log
Hmm, using 0x29 = 41 results in -3. […]
Yeah I can't remember where the original 0x29 value came from, but that is what was used to validate on Volteer before I found this algorithm in a doc. I can't easily repro the original issue (no cell service at home) so I can't test 0x2a myself with the original issue but I imagine it wouldn't make much difference.
I suspect other platforms that are setting 0 for the default may have the same issue that TGL has, but it is going to be hard to verify without USB test equipment or a reproduction case like we had on Volteer.
As far as I can tell FSP is checking Usb3HsioTx*Enable==TRUE before applying any settings, and these UPDs all default to 0 so nothing will get applied unless coreboot sets it up.