Technically it is possible, Intel platforms since Haswell can do it. As for the support of the Ryzen 5xxx CPUs with 4xx series chipsets, it is up to ASUS to consider (because let us remember it anyway for certain, it is not a non-profit NGO ...) if it is more interesting to make shine brand image with gamers by activating this feature where possible (despite most motherboards being mostly EoL), or rather artificially restricting this feature to the latest motherboards to sell more.
In addition, to date this feature only affects new AMD graphics cards, knowing that over 70% of gamers use NVIDIA graphics cards (Steam statistics) and that NVIDIA is working on it only for his RTX 3xxx series GPUs, there is no point in being rushed for the most part.
To date here are the chipsets which have BIOS with BAR/SAM :
- 5xx series chipsets (Example : https://rog.asus.com/motherboards/rog-strix/rog-strix-x570-f-gaming-model/helpdesk_bios/)
- 4xx series chipsets (Example : https://rog.asus.com/motherboards/rog-strix/rog-strix-x470-f-gaming-model/helpdesk_bios/)
- 4xx series chipsets (Example : https://rog.asus.com/motherboards/rog-strix/rog-strix-z490-f-gaming-model/helpdesk_bios/)
- X299 chipset - Beta (Example : https://rog.asus.com/forum/showthread.php?121843-Will-resizable-bar-(smart-access-memory-alternative...)
Would definitely like to see Resize BAR offered in Z370/Z390, as those mobos are still running abundant in use.
they do not even add additional memory settings as in z490 in bios 390 as msi did, I doubt it, but it is possible even on older processors this technology works in linux and it is not exclusive to amd