Update preserve_rom function to check if /tmp/cbfs-init.rom should be used.

[mdrobnak]

On the MSI boards, the "internal" CBFS region, which is the default when calling cbfs without arguments, returns no files, or when called with -v, errors:

Header delta          : -29261268
Header magic          : ffffffff
Header version        : ffffffff
Header ROM size       : ffffffff
Header boot block size: ffffffff
Header align          : ffffffff
Header offset         : ffffffff
Header arch           : ffffffff
Failed to find valid header

This patch is an extension of linuxboot@4d533b3 changes, which if configured uses flashrom to extract the image of the CBFS there, and here it uses that extracted image to add files to the image which is to be flashed.

This has been tested on my MSI Z790-P DDR4 board.

[mdrobnak]

Closing in favor of linuxboot#1699

[tlaurion]

@mkopec the ideal fix would be to extend cbfs.c capabilities as discussed under linuxboot#1699 (comment). Thoughts?

[mdrobnak]

Re-opening here. This will fix any MSI users for the time being.

[tlaurion]

@mkopec the ideal fix would be to extend cbfs.c capabilities as discussed under linuxboot#1699 (comment). Thoughts?

@mkopec is upstreaming MSI boards under linuxboot/heads planned short term?

[mkopec]

Thank you for the fix! As we discussed elsewhere, ideally we'd add support for the extended BIOS window to flashtools and not use flashrom, but I have no problem merging this for now.

[mkopec]

@mkopec is upstreaming MSI boards under linuxboot/heads planned short term?

paging @macpijan

[tlaurion]

@macpijan needs upstreaming alongside MSI boards.

[tlaurion]

linuxboot#1699 : put as draft. Please refer to that PR upstream with a PR that deprecates it.

[tlaurion]

Opened Dasharo/dasharo-issues#897 to track