usb: hub: Disable USB 3 device initiated lpm if exit latency is too high

commit 1b7f56fb

 upstream.

The device initiated link power management U1/U2 states should not be
enabled in case the system exit latency plus one bus interval (125us) is
greater than the shortest service interval of any periodic endpoint.

This is the case for both U1 and U2 sytstem exit latencies and link states.

See USB 3.2 section 9.4.9 "Set Feature" for more details

Note, before this patch the host and device initiated U1/U2 lpm states
were both enabled with lpm. After this patch it's possible to end up with
only host inititated U1/U2 lpm in case the exit latencies won't allow
device initiated lpm.

If this case we still want to set the udev->usb3_lpm_ux_enabled flag so
that sysfs users can see the link may go to U1/U2.

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210715150122.1995966-2-mathias.nyman@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>