[XS] Change in flashrom[main]: erasure_layout: Erase larger block only when all sub-block need erase

[Bill XIE (Code Review)]

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Bill XIE has posted comments on this change by Bill XIE. ( https://review.coreboot.org/c/flashrom/+/84614?usp=email )

Change subject: erasure_layout: Erase larger block only when all sub-block need erase
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Patch Set 1:

(1 comment)

Patchset:

PS1:
> I would call it "nested sub-blocks" instead of "double sub-blocks", what do you think?

Okay. I will change the commit message later.
> p.1 is a good question to discuss. My understanding, the idea was that if we have a region, and there are many small blocks inside that need erase, maybe it's faster to send one opcode once, and erase the whole region (instead of sending lots of opcodes for each small region).

My consideration is to reduce the wearout as much as possible like the old version of flashrom before erasure_layout.c was introduced, so a block needless to erase is never erased.
> And before the patch the threshold was 50% , you changed it to 100%.

I am thinking that maybe the optimal is in between?

I will never consider to exchange programming speed with chip lifetime 😞, so we may leave it for the end user to decide: We may add a (command line) option to specify "extra erase ratio"--the percentage of overall sub-blocks needless to erase within a larger erase block to be sacrificed for programming speed, default 0, max 100 (meaning whole chip erase 😜).