MSI's latest BIOS update cuts support for Bristol Ridge APUs in some AM4 A320 motherboards
The Socket AM4 platform has proven to be very successful for AMD in terms of increased compatibility of CPUs right from Bristol Ridge and Carrizo Pro APUs to the present day Ryzen CPUs and APUs. However, motherboard manufacturers are increasingly finding it difficult to accommodate backward compatibility for all socket AM4 processors. In the latest BIOS update for one of its A320 motherboards, MSI has contraindicated the update for users running AMD Bristol Ridge APUs.
According to MSI's changelog for BIOS version 7B07v3G1 (beta) for the A320M Pro-VH Plus motherboard, the 'upcoming AMD CPU' is supported but several Bristol Ridge A-series APUs have been excluded. This means users with these older APUs should refrain from updating their BIOS and exercise caution with any future BIOS update.
The issue of supporting legacy CPUs on newer AMD motherboards has been going on for quite sometime now. While AMD has promised support for socket AM4 and backward compatibility of new Ryzen CPUs with the socket at least till 2020, it is really up to the motherboard OEMs to decide on the support path. For supporting six generations of about 55+ AM4 chips, the BIOS microcode needs to contain instructions for all of them leading to bloated firmware that doesn't fit on smaller chips.
Low-end motherboards usually ship with smaller capacity BIOS chips that can quickly prove to be limiting for newer microcode versions that offer support for the latest processors. OEMs have two choices here — either increase the size of the BIOS chip or cut down on legacy CPU support. Increasing the size of the BIOS chip would entail higher costs, which can put low-end motherboards at a price disadvantage so OEMs usually prefer culling support for legacy processors to ensure that updated microcode can still be accommodated in the limited storage space.
The BIOS size issue appears to be confined to just low-end motherboards for now and it remains to be see how many A320 boards will be getting support for Ryzen 3000. May be reducing some of the flashy UEFI interface elements could help in circumventing the issue for the time being.