ehci: bound all init waits; stop auto-rescanning; wider boot watchdogqemu

Hardware run 3 showed the same PED=0 SETUP halt and then never reached the
prompt.  Two boot-time hazards explain the death:

- reset_port polled PED with a 2,000,000-iteration MMIO loop (seconds on real
  silicon) and the reset retry ran it twice per port, so the port scan alone
  exceeded the boot watchdog window (task 0 in one frame for 7.5 s panics).
- while no HID was found the cursor task re-ran the whole EHCI scan, port
  resets included, every second -- a rate-matching hub never settles.

Changes:
- every EHCI wait is wall-clock bounded: halt/reset/run 500 ms, PED 200 ms
- control-transfer timeout 5 s -> 500 ms
- per-controller 3 s port-scan budget; no automatic re-scan (explicit
  `usb rescan` only)
- 300 ms power-up settle before the reset walk (RMH bring-up)
- boot-phase watchdog 750 -> 2000 ticks (20 s), room for hub bring-up
- xHCI gets the same persistent bottom-row port/device summary

1 files changed, 19 insertions, 1 deletions

diff --git a/rsnix/src/usb.rs b/rsnix/src/usb.rs
index 5a4136f..aa41b0e 100644
--- a/rsnix/src/usb.rs
+++ b/rsnix/src/usb.rs
@@ -699,6 +699,7 @@ fn enumerate(port: u32, speed: u32) -> bool {
     }
     NXDEV.fetch_add(1, Ordering::Relaxed);
     queue_report(idx);
+    show_summary();
     crate::serial_println!(
         "usb: HID {} armed (slot {} mps {} interval {})",
         if kind == Kind::Mouse { "mouse" } else { "keyboard" },
@@ -968,10 +969,12 @@ pub fn init() -> bool {
         }
     }
     INITOK.store(true, Ordering::Relaxed);
+    let ports = unsafe { MAXPORTS };
     crate::serial_println!(
         "usb: controller up ({} ports) — HID discovery deferred to polling",
-        unsafe { MAXPORTS }
+        ports
     );
+    show_summary();
     true
 }
 
@@ -1008,6 +1011,21 @@ fn maybe_discover() {
     }
 }
 
+/// Persistent bottom-row summary for hardware runs without serial.
+fn show_summary() {
+    let (np, nd) = unsafe { (MAXPORTS, NXDEV.load(Ordering::Relaxed)) };
+    let mut line = alloc::format!("xhci ports={} devs={}:", np, nd);
+    unsafe {
+        for p in 0..np.min(8) {
+            let v = rd(op(OP_PORTSC) + (p as usize) * PORT_STRIDE);
+            if v & PORT_CONNECT != 0 {
+                line.push_str(&alloc::format!(" p{}={:04x}", p, v & 0xffff));
+            }
+        }
+    }
+    crate::gop::boot_marker_at(&line, crate::gop::bottom_row(3));
+}
+
 fn has_kind(kind: Kind) -> bool {
     let n = NXDEV.load(Ordering::Relaxed) as usize;
     for i in 0..n {