[M] Change in coreboot[master]: mb/google/rex: Update Flash Layout to fit WP_RO within 4MB

[Subrata Banik (Code Review)]

Attention is currently required from: Tarun Tuli, Paul Menzel.

Subrata Banik has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/74229 )

Change subject: mb/google/rex: Update Flash Layout to fit WP_RO within 4MB
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Patch Set 5:

(3 comments)

Commit Message:

https://review.coreboot.org/c/coreboot/+/74229/comment/9a55efe3_c61639b1 
PS1, Line 9: This patch updates the Rex flash layout to optimize WP_RO to 4MB.
> > The board was apparently added with 8 MB, so why is it too big now? What optimization is done?
>
> Sorry, I'm still unable to understand what details, u would like to know? we had goal to drop WP_RO from 8MB to 4MB at some point of the program and now we are doing so.

i have updated the commit section to add the motivation towards this change.

https://review.coreboot.org/c/coreboot/+/74229/comment/c15524fe_d350ea87 
PS1, Line 9: This patch updates the Rex flash layout to optimize WP_RO to 4MB.
           : 
           : Changes for chromeos.fmd:
           : 
           : SI_BIOS:
           :      RW_SECTION_A/B: Reduce to 7MB.
           :      RW_LEGACY: Reduce to 1MB.
           :      RW_MISC: Increased to 1MB.
           :      RW_UNUSED: 3MB (reserved)
           :      WP_RO: Reduce to 4MB
           : 
           : Additionally, ensure RW_SECTION_B region starts at 16MB boundary in the
           : SPI Flash.
> > I am sorry you are feeling this way.
>
> I would like to understand if your intention is code review, then please help on that part. I'm feeling like, u are suggesting something which is not possible and I have explained why so, but still this conversation continues

@Paul, marking as done. please let me know otherwise.

File src/mainboard/google/rex/chromeos.fmd:

https://review.coreboot.org/c/coreboot/+/74229/comment/2f87bbbe_13a7d393 
PS1, Line 7: 7M
> > Changing 7092K to 7M is cosmetic, isn’t it?
>
> @Paul, you have to understand every bytes are meaningful here. I can't just drop 92K in one CL without adding those 92K to any other region.

@Paul, i'm marking this done. please let me know otherwise