Attention is currently required from: Sathyanarayana Nujella, Varshit B Pandya, Subrata Banik, Francois Toguo Fotso, Maulik V Vaghela, Paul Menzel, Angel Pons, Ronak Kanabar, Jairaj Arava, Patrick Rudolph. Furquan Shaikh has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/51353 )
Change subject: soc/intel/alderlake: Update iDisp Link UPD settings ......................................................................
Patch Set 7:
(1 comment)
Commit Message:
https://review.coreboot.org/c/coreboot/+/51353/comment/d2bf51af_e8cecff5 PS6, Line 9: These UPD values are automatically set by the FSP.
from previous platform on, the decision has been made to leave these UPD with their default values a […]
There is no explanation in CB:40263 as well about why we should just leave the UPDs at their default. b/151451125 has some details based on which it looks like these UPDs need to be set to these defaults: T-mode: 4T Link frequency: 96MHz
However, `PchHdaIDispCodecDisconnect` should be set to 0 only if mainboard wants to enable display audio. Yes, I agree this is true for Chrome OS devices, but I don't think we should just keep this enabled for all other devices in upstream coreboot. It should still be left to the mainboard to decide this.
I think the way this should be handled is:
1. Have a devicetree config `enable_display_audio`. 2. If a mainboard selects `enable_display_audio` in the devicetree, then SoC common code should set UPDs as follows: ``` PchHdaIDispLinkTmode -> 4T PchHdaIDispLinkFrequency -> 96MHz PchHdaIDispCodecDisconnect -> 0 ``` If `enable_display_audio` is not set by mainboard, then set `PchHdaIDispCodecDisconnect` to 1 indicating mainboard does not want to enable display audio.
3. Set `enable_display_audio` to 1 for Chrome OS devices (this would be adlrvp and baseboard devicetree for brya).
This will ensure that the relevant UPDs are configured correctly based on mainboard selection. If we ever see a platform that needs to adjust Tmode/frequency, devicetree configs can be added for those. But for now, we can skip those two.