> Hint: on x86 it's essentially one billion instructions before you can even think about using RAM, much less loading the payload.
This is why everybody using INTEL silicon do have FSP as A MUST (instead SEC+PEI). And this is why CORE CPU creations (2C+) have > 500 million gates per silicon. There gazillions of modes, which are probably only 10% used in real scenarios. All others are testing modes. And INTEL made smart investment forcing customers to pay for that (excessive silicon use/overkill).
> which is to load linux from flash. It's working fine on UEFI today and
I'm seeing what it takes to replace the coreboot ramstage with linux.
YUP. Since no OS loader, only one/single OS instance to be actually loaded from flash. Then you don't care about AHCI, SATA, IDE and other HDD/SSD modes, also about GFX (embedded Linux) and also CSM or UEFI. No INT, no Run Time Services. You are running true ram disk, unpacked from flash as well.