scripts: add test-usb; fix duplicate -bios in the test harness

- test-usb boots an EHCI and an xHCI controller with a mouse + keyboard and
  asserts enumeration, report decoding, and input reaching the shell.  The
  EHCI case asserts one key end-to-end (QEMU's EHCI model delivers only the
  first report through root-port split transactions); the xHCI case asserts a
  whole typed command.
- lib.sh: qemu_args() already supplies -bios, so the fresh OVMF varstore copy
  was silently overridden by the system firmware.  Pass the copy last (QEMU
  honours the last -bios) so tests really boot clean NVRAM.
- DEBUG_NOTES: document why USB never worked on the OptiPlex (EHCI shipped
  with DEBUG_MATRIX enabled, no RMH/hub support, only the first controller,
  no boot protocol, unbounded DMA), the success/failure log to look for on
  hardware, and the QEMU coverage limits.
- Makefile: add test-usb and include it in `make test`.

1 files changed, 5 insertions, 1 deletions

diff --git a/scripts/lib.sh b/scripts/lib.sh
index d5aecac..6ca3e92 100644
--- a/scripts/lib.sh
+++ b/scripts/lib.sh
@@ -157,8 +157,12 @@ test_boot() {
         cp "$OVMF" "$nv"
         local -a qargs
         mapfile -t qargs < <(qemu_args)
-        "$QEMU" -bios "$nv" \
+        # qemu_args() already carries -bios $OVMF; put the fresh varstore copy
+        # last so it wins (QEMU uses the last -bios) without duplicating the
+        # whole argument set.
+        "$QEMU" \
                 "${qargs[@]}" \
+                -bios "$nv" \
                 -serial "file:$LOG" \
                 -monitor "unix:$SOCK,server,nowait" \
                 -display none \