usb: hub: fix detection of high tier USB3 devices behind suspended hubs

USB3 devices connected behind several external suspended hubs may not
be detected when plugged in due to aggressive hub runtime pm suspend.

The hub driver immediately runtime-suspends hubs if there are no
active children or port activity.

There is a delay between the wake signal causing hub resume, and driver
visible port activity on the hub downstream facing ports.
Most of the LFPS handshake, resume signaling and link training done
on the downstream ports is not visible to the hub driver until completed,
when device then will appear fully enabled and running on the port.

This delay between wake signal and detectable port change is even more
significant with chained suspended hubs where the wake signal will
propagate upstream first. Suspended hubs will only start resuming
downstream ports after upstream facing port resumes.

The hub driver may resume a USB3 hub, read status of all ports, not
yet see any activity, and runtime suspend back the hub before any
port activity is visible.

This exact case was seen when conncting USB3 devices to a suspended
Thunderbolt dock.

USB3 specification defines a 100ms tU3WakeupRetryDelay, indicating
USB3 devices expect to be resumed within 100ms after signaling wake.
if not then device will resend the wake signal.

Give the USB3 hubs twice this time (200ms) to detect any port
changes after resume, before allowing hub to runtime suspend again.

Cc: stable <stable@kernel.org>
Fixes: 2839f5bcfcfc ("USB: Turn on auto-suspend for USB 3.0 hubs.")
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20250611112441.2267883-1-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

0 files changed, 0 insertions, 0 deletions