Hi
link went to U3. Why would xhci put the link to U3 now? We're still
working fine.
This looks like a pretty crazy set of transitions. I'm unfamiliar with
LPM. Is this sequence of events normal for a transition to U3?
See figure 7-14 on USB 3.1 spec. This shows that from U2 we had LFPS
timeout which forced link to SS.Inactive. Then, link *must* go through
RX.Detect to restart a session. From there, a condition called RX Detect
Overlimit happens, which forces the port to SS.Disabled.
Link is, then, moved to U0 by the host. Then RX.Detect, then U3. This is
all under host side control. DWC3 is simply reporting the states.
During this particular run, I was not performing any operations on the
mass storage device besides mounting it on my computer. No reading or
writing besides that. Would this sort of inactivity have something to do
with the transition to U3?
No. XHCI shouldn't put anything into U3 by default. Mathias can give
more details here.
So System and runtime suspend sets link to U3, but it is also set for USB3
devices when we want to disable the device.
This is because USB3 does not have any "disabled" link state like USB2 that will
avoid negotiating a connection with a plugged-in cable, and signal the host
when the cable is unplugged.
This is done when the device is ejected/safely removed, or in case something already
went wrong and we want to "disable" the device.
-Mathias
