[coreboot] Flash ROM access during boot

[Peter Stuge]

Paul Menzel via coreboot wrote:
> Are there ways or strategies to preload the whole flash ROM chip
> content into memory for faster access right after RAM is set up for
> example? What does that depend on? Does that make any sense at all?

That's called BIOS shadowing and was popular at least in the 90s.

I'm sure hardware still supports it, but I don't know if it makes a
lot of sense.

If the trace shows a large number of random accesses in ramstage then
it might make a significant difference, but I suspect it's not really
a bottleneck.

The payload should be read using memcpy() anyway, so that wouldn't
benefit.

And reading the entire chip only for ramstage doesn't make sense.

Finally, modern chipsets can and will prefetch at least some amount
of flash contents, but maybe only a small number of bytes. I remember
reading 16 bytes somewhere.


//Peter