[coreboot] cmos.layout upgradability

[mrnuke]

On Saturday, January 25, 2014 12:51:25 AM Vladimir 'φ-coder/phcoder' 
Serbinenko wrote:
> Hello, all. Due to my failue to foresee this problem if one upgrades X60
> coreboot, you need to manually reset CMOS config or your trackpad may
> not work as option "trackpad_enable" will get a garbage value. While I
> admit my part of fault, I feel like we should have a way to update
> options safely. I see following possibilities:
> 1) Hide ourselves and tell that on upgrade you always have to clear
> CMOS. I don't think it's really an option as users will continue just
> running flashrom and in case of external flashing, CMOS reset may
> require full power removal with cell battery sometimes in difficult to
> access places inside laptop.
> 2) Have some version field to check and if it mismatches reset CMOS to
> default. To avoid having to maintain version manually I propose to
> checksum option table and write 16-bit result to CMOS. 16-bit should
> give enough confidence without excessively using CMOS. I've made a
> prototype at http://review.coreboot.org/#/c/4790/4 . If we can agree
> that it's a right approach, I'll make this prototype into complete patch
> (mostly missing is laborous adding of version field)
> 2a) instead of having separate field we could make XOR layout checksum
> into CMOS checksum. This would save 2 bytes but will break any existing
> users if they check checksum.

You mean it won't write the cmos.default after upgrade?

And why would you need to reset CMOS if trackpad is disabled?

 # nvramtool -a
 # nvramtool -w trackpad_enable=Enable