mb/google/puff: program RTL8168 MAC into ERI

[jackadam1981]

Summary

This fixes the PXE MAC address on Google Puff-derived KAISA systems (Acer Chromebox CXI4) with the onboard Realtek RTL8111/8168 controller.

On the tested KAISA unit, Linux still reported the correct VPD-backed MAC address, but the firmware PXE path showed an all-zero MAC address (00:00:00:00:00:00). The board already selects RT8168_GET_MAC_FROM_VPD, so coreboot reads the right address, but the RTL8168 hardware also needs the address programmed into the ERI registers for this controller revision before the PXE stack uses it.

Changes

• Select RT8168_PUT_MAC_TO_ERI for the Puff baseboard so KAISA programs the VPD MAC into the controller ERI registers.
• Treat PCI revision ID 0x15 / decimal 21 like revision 9 in the RTL8168 ERI MAC programming path.

Hardware details

The tested onboard NIC is:

Realtek RTL8111/8168/8211/8411 PCI Express Gigabit Ethernet Controller [10ec:8168] (rev 15)

rev 15 is hexadecimal, so this is PCI revision ID 0x15 / decimal 21, matching the new case 21 path.

Validation

Built a 2603 release ROM for KAISA with PXE + iPXE enabled, using the MrChromebox 2603 coreboot/EDK2 sources plus this two-line change.

Test ROM:

coreboot_edk2-kaisa-mrchromebox_2603_release_pxe_ipxe_rt8168_eri_rev21_20260528-142302.rom
sha256: 5258185a9a1419d6bb17f1c7c7a7dd4a2b2fed28fd361b33f5981ae324ffd503

Flashed on a real Acer Chromebox CXI4 / KAISA using the MrChromebox firmware utility. The utility preserved VPD, RW_MRC_CACHE, and SMMSTORE during the custom flash. After reboot, the PXE screen showed the MAC address instead of all zeros.

[MrChromebox]

this looks good, I think I'll break this up into 2 commits, and apply it to other chromeboxes with RT81xx. Fizz uses Rev 0x15 as as well, I need to check the others.

[MrChromebox]

here's what I upstreamed, thoughts? https://review.coreboot.org/c/coreboot/+/93049

[MrChromebox]

the above patch series has been cherry-picked back into 2603