feat: devices via caps (BootInfo, init assigns devices, drivers map MMIO/DMA themselves, IRQ-driven input); drop boot device wiring and info pages; headless display fallback

docs/ipc.md

@@ -73,6 +73,28 @@ one region, so delegating or revoking it means the same thing everywhere.
 `RegionAddress(cap)` returns a region's physical base so a driver can
 program a device's DMA; pool regions are physically contiguous.
 
+Boot also maps one read-only page into init at `types::bootinfo::BOOT_INFO_VA`
+listing, for each board device, its kind, physical base, IRQ line and the
+slots holding its region and IRQ capabilities, plus the SystemControl slot.
+It is the only page boot writes for userspace.
+
+## Devices
+
+Init decides which driver gets which device: it asks each virtio slot for
+its device id (mapping a minted copy of the region capability, then
+dropping it), and hands the disk, GPU and keyboard (or, with no keyboard,
+the UART) to their drivers before anything else (`libkos::device`):
+
+1. init `Call`s the driver's endpoint `[SETUP, MMIO, kind]` carrying the
+   region capability, then `[SETUP, IRQ]` with the IRQ capability, then
+   `[SETUP, DONE]`. A driver with no device gets only `DONE`.
+2. The driver maps the region, allocates its own DMA memory
+   (`CreateRegion`, `MapRegion`, `RegionAddress`) and resets the device.
+3. A driver with an IRQ routes it to a notification bound to its thread
+   (`SetIrqNotification`, `BindNotification`) and acknowledges once to arm
+   it. Lines start masked, are masked again by the kernel on every
+   interrupt, and are re-armed by `AckInterrupt`.
+
 ## Messages
 
 A message is 4 words and at most one capability. The capability is