I'm not thrilled with this solution.
The standard pre-pmap_bootstrap() KVA is 128 MB, including:

• kernel text/data/bss (section-mapped from KERNBASE);
• early page tables (kern_pt1, kern_pt2tab and initial L2 pages);
• whatever initarm() takes (dpcpu, stacks, msgbuf, etc.).

So there are only tens of megabytes of free KVA for the framebuffer.

Another thing: Wouldn't it be much cleaner to extend the implementation of pmap_mapdev_attr() for early boot phase of armv7? subr_devmap.c looks ready for this job.

In D59264#1359759, @mmel wrote:

Another thing: Wouldn't it be much cleaner to extend the implementation of pmap_mapdev_attr() for early boot phase of armv7? subr_devmap.c looks ready for this job.

should we even pull in kib@ or someone else to talk about the kvm layout and pmap stuff?

-a