[S] Change in coreboot[main]: nb/intel/haswell: make IOMMU a runtime option

[Paul Menzel (Code Review)]

Attention is currently required from: Alexander Couzens, Angel Pons, Leah Rowe.

Paul Menzel has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/81016?usp=email )

Change subject: nb/intel/haswell: make IOMMU a runtime option
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Patch Set 1:

(2 comments)

Commit Message:

https://review.coreboot.org/c/coreboot/+/81016/comment/3f7f36b3_3b1417dc :
PS1, Line 9: When I tested graphics cards on a coreboot port for Dell
           : OptiPlex 9020 SFF, I could not use a graphics card unless
           : I set iommu=off on the Linux cmdline.
Any idea why? What Linux version is that?

https://review.coreboot.org/c/coreboot/+/81016/comment/6500f47b_6e36144a :
PS1, Line 9: When I tested graphics cards on a coreboot port for Dell
           : OptiPlex 9020 SFF, I could not use a graphics card unless
           : I set iommu=off on the Linux cmdline.
           : 
           : The current coreboot behaviour is to check whether the CPU
           : has vt-d support and, if it does, initialise the IOMMU.
           : 
           : This patch maintains the current behaviour by default, but
           : allows the user to turn *off* the IOMMU, even if vt-d is
           : supported by the host CPU.
           : 
           : If iommu=Disable is specified, the check will not be
           : performed, and the IOMMU will be left disabled. This option
           : has been added to all current Haswell boards, though it is
           : recommended to leave the IOMMU turned on in most setups.
           : 
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