Replace the polling-only main loop with interrupt-driven change
detection modeled on Linux 7.1 hub_irq().
Key changes:
1. Discover the hub's interrupt IN endpoint from the interface
descriptor (typically EP1 for USB 2.x, may be absent for USB 3).
Use EndpointTy::Interrupt + EndpDirection::In to match.
2. Open the endpoint via XhciClientHandle::open_endpoint(1) and
call transfer_read() to receive the status-change bitmap.
3. Build a per-port change mask from the bitmap:
Port N is bit (N-1) of byte (N-1)/8. Only ports whose bit is
set in the mask are polled for detailed GetPortStatus.
4. Graceful fallback: if the interrupt endpoint is absent or the
transfer fails, fall back to polling all ports at 200ms.
5. Interrupt-driven mode blocks on transfer_read() — no explicit
sleep needed. Polling mode sleeps 200ms per cycle (was 250ms,
tightened from 1000ms in P3 slice 1).
6. Added XhciEndpHandle import for endpoint operations.
Cross-reference: Linux 7.1
- drivers/usb/core/hub.c: hub_irq() — URB completion handler
- drivers/usb/core/hub.c: hub_configure() — interrupt endpoint setup
- include/linux/usb/ch11.h — hub status change bitmap format
This completes P3 hub maturity — power-on timing (slice 1) plus
interrupt-driven detection (slice 2) brings usbhubd to Linux 7.1
parity for the two most important hub operations.
First P3 hub-driver maturity improvements, cross-referenced with
Linux 7.1 drivers/usb/core/hub.c:
1. Power-on timing (hub_power_on + hub_power_on_good_delay)
- reads bPwrOn2PwrGood (V2: power_on_good; V3: default 10)
- sleeps power_on_good * 2ms after SET_FEATURE(PORT_POWER)
- minimum floor: 100ms (matches Linux hub_power_on_good_delay)
- logs the computed delay at startup
2. USB 3 hub stall fix
- ConfigureEndpointsReq no longer passes interface_desc or
alternate_setting for USB 3 hubs
- xHCI handles default-alt-0 derivation internally
- resolves the two TODOs that documented the stall symptom
3. SET_HUB_DEPTH with hub_depth() value
- previously passed port_id.hub_depth().into() which was
incorrect (returned route-string-derived depth)
- now logs the depth value explicitly
4. Polling interval tightened 1s -> 250ms
- interrupt-driven detection remains a follow-up (P3 slice 2)
- 250ms is a reasonable intermediate step for USB keyboard
responsiveness
5. wHubDelay recorded from V3 descriptor
- extracted from hub_desc.delay field
- displayed at startup; future P3 slices will accumulate
through the hub tree per Linux hub_configure()
Cross-reference: Linux 7.1
- drivers/usb/core/hub.c: hub_power_on()
- drivers/usb/core/hub.c: hub_power_on_good_delay()
- drivers/usb/core/hub.c: hub_activate()
- include/linux/usb/ch11.h: HUB_SET_DEPTH = 0x0C
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