[coreboot] [SeaBIOS] 5 basic features provided by CSM, which SeaBIOS does provide?

[Kevin O'Connor]

On Mon, Dec 21, 2015 at 12:57:33PM +0000, Stojsavljevic, Zoran wrote:
> Hello Kevin,
> 
> All Good with setting CSM ON for legacy support. You need it for 16 bit BIOSes, and for legacy OSes, such as WIN XP or WIN 7 and derivatives.
> 
> Here is the question I am wondering: What if I decide to bring FSP -> Coreboot -> SeaBIOS -> WIN 8.1 32. Do I really need SeaBIOS with option set to: CSM ON (I brought WIN 8.1 32  on CC2 with SeaBIOS and feature CSM ON)? In other words, can I bring WIN 8.1 32 on FSP -> Coreboot -> SeaBIOS with CSM OFF?
> 
> The same question for: FSP -> Coreboot -> SeaBIOS -> WIN 8.1 64? I guess, here is CSM ON mandatory. Am I correct?
> 
> Could I have a true 32 or 64 UEFI compliant OS on BSP: FSP -> Coreboot -> SeaBIOS -> UEFI OS sans/without CSM feature ON? The same one I have after bringing on UEFI 32/64 BIOS UEFI 32/64 OS (CSM is OFF always)?  
> 

In all of the above situations you must compile SeaBIOS with
CONFIG_COREBOOT=y and CONFIG_CSM=n.  CONFIG_CSM is mutually exclusive
with CONFIG_COREBOOT, and if one is planning to run SeaBIOS directly
from coreboot then one must use CONFIG_COREBOOT=y.

-Kevin