Probe failure of usb controller @11290000 on MT8195 after next-20231221

[Nícolas F. R. A. Prado]

Hi,

KernelCI has identified a failure in the probe of one of the USB controllers on
the MT8195-Tomato Chromebook [1]:

[   16.336840] xhci-mtk 11290000.usb: uwk - reg:0x400, version:104
[   16.337081] xhci-mtk 11290000.usb: xHCI Host Controller
[   16.337093] xhci-mtk 11290000.usb: new USB bus registered, assigned bus number 5
[   16.357114] xhci-mtk 11290000.usb: clocks are not stable (0x1003d0f)
[   16.357119] xhci-mtk 11290000.usb: can't setup: -110
[   16.357128] xhci-mtk 11290000.usb: USB bus 5 deregistered
[   16.359484] xhci-mtk: probe of 11290000.usb failed with error -110

A previous message [2] suggests that a force-mode phy property that has been
merged might help with addressing the issue, however it's not clear to me how,
given that the controller at 1129000 uses a USB2 phy and the phy driver patch
only looks for the property on USB3 phys.

Worth noting that the issue doesn't always happen. For instance the test did
pass for next-20240110 and then failed again on today's next [3]. But it does
seem that the issue was introduced, or at least became much more likely, between
next-20231221 and next-20240103, given that it never happened out of 10 runs
before, and after that has happened 5 out of 7 times.

Note: On the Tomato Chromebook specifically this USB controller is not connected
to anything.

[1] https://linux.kernelci.org/test/case/id/659ce3506673076a8c52a428/
[2] https://lore.kernel.org/all/239def9b-437b-9211-7844-af4332651df0@xxxxxxxxxxxx/
[3] https://linux.kernelci.org/test/case/id/65a8c66ee89acb56ac52a405/

Thanks,
Nícolas