CML v1 / v2 FSP

Jonathon Hall <[email protected]>
Newsgroups gmane.linux.bios
Message-ID <[email protected]>
Hi all,

As many of you probably know, Comet Lake v1/v2 have different FSP 
binaries, and hence separate Kconfigs `SOC_INTEL_COMETLAKE_1` and 
`..._2`.  In short, the same SKU could be either depending on the stepping.

We're getting new steppings in future batches of products, which will 
move them from CML v1 to CML v2.  These aren't otherwise "new versions" 
of the product.  It would simplify life for my customers if they had the 
same firmware image.

 From an initial look it seems reasonable to embed both FSPs and select 
at runtime using the CPUID as suggested by Intel:
* The headers for both FSPs are equivalent (differ only in comments), so 
there should be no issue switching at runtime
* The _1 / _2 Kconfigs are only used to select FSP headers/binary, 
nothing else
* It'll cost some flash space, so separate _1 / _2 should continue to 
exist, but in my case that tradeoff is fine

Has anyone looked into this in the past?  Is there any other reason this 
is not a good idea?

 From my initial look, I would try:
* Add another Comet Lake Kconfig, say `SOC_INTEL_COMETLAKE_1_2` (or 
`..._1_AND_2`, etc.)
* Embed a second FSP - probably add an optional `FSP_FD_PATH_2` to the 
FSP 2.0 Kconfig, the `..._1_2` SoC Kconfig would then put its second FSP 
here
* Add a second `FSP_M_CBFS`/`FSP_S_CBFS` (the names of the files in cbfs)
* For `SOC_INTEL_COMETLAKE_1_2`, select the correct cbfs name based on 
CPUID.  Those are only used in a few places, so the impact wouldn't be 
very large.

Thanks,
Jonathon

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