Kick off the display service track (docs/display.md, docs/display-plan.md): a
user-space compositor that owns the framebuffer. GOP and the PCI display device
are two views of one controller; GOP dies at ExitBootServices, so the portable
base is the boot-handoff linear framebuffer.
D1 makes that framebuffer reachable from user space over the existing device
claim/mmio_map path rather than a bespoke syscall:
- device-abi: a `display` DeviceClass, a DisplayInfo{w,h,pitch,format} on the
descriptor, and a flags field on resources with a write-combining bit.
- devices-broker: seedDisplay() publishes the loader's framebuffer as a
root-level `display` node (one WC-flagged memory resource); kmain seeds it
after discovery. displayDevice()/displayClaimed() track the claim.
- paging/mmio_map: mapUserDeviceInto gains a write_combining bool — a WC-flagged
resource maps through PAT entry 4 instead of strong-uncacheable (an
uncacheable framebuffer blit is glacial).
- console: falls silent while a display service holds the framebuffer, and is
forced back on by the panic/exception paths.
Gate: the `display` kernel test asserts the seeded node's shape and that the
claim + mmio_map leaf is genuinely write-combining (PAT bit set, PCD/PWT clear).
Regression-checked discovery/ioport/claim-release/supervision/device-list/
device-manager with the +1 device in the table.
Daniel Samson