[coreboot-gerrit] Change in coreboot[master]: drivers/smmstore: Implement SMMSTORE version 2

[Patrick Rudolph (Code Review)]

Patrick Rudolph has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/40520 )

Change subject: drivers/smmstore: Implement SMMSTORE version 2
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Patch Set 19:

(1 comment)

https://review.coreboot.org/c/coreboot/+/40520/1/src/include/smmstore.h 
File src/include/smmstore.h:

https://review.coreboot.org/c/coreboot/+/40520/1/src/include/smmstore.h@40 
PS1, Line 40: * Version 2 of the SMM requires as SMMSTORE of at least 256KiB of size, that
            :  * has to be aligned to 64KiB.
            :  * This allows the payload to store raw data in the SMMSTORE flash region.
            :  * This can be used by a FaultTolerantWrite implementation, that uses at least
            :  * two regions in an A/B update scheme.
> 64KiB is the minimum for UEFI variable store + 64KiB as FaultTolerantWrite backup. […]

There are usually 3 regions used by EDK.
* The variable store
* The FTW spare block
* The FTW working block

All regions must be block aligned.
The FTW Spare size must be greater than the variable store. In this case 64KiB + 1 block.
The FTW Working Size can be much smaller than 64KiB.

That sums up to:
* The variable store: 1block = 64KiB
* The FTW spare block: 2blocks = 2x64KiB
* The FTW working block: 1block = 64KiB
In total 256KiB that's required when using 64KiB block size and EDK2 variable store.