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

[Nícolas F. R. A. Prado]

On Fri, Jan 19, 2024 at 10:12:07AM +0100, AngeloGioacchino Del Regno wrote:
> Il 18/01/24 19:36, Nícolas F. R. A. Prado ha scritto:
> > 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
> 
> Hey Nícolas,
> 
> I wonder if this is happening because of async probe... I have seen those happening
> once in a (long) while on MT8186 as well with the same kind of flakiness and I am
> not even able to reproduce anymore.
> 
> For MT8195 Tomato, I guess we can simply disable that controller without any side
> effects but, at the same time, I'm not sure that this would be the right thing to
> do in this case.
> 
> Besides, the controller at 11290000 is the only one that doesn't live behind MTU3,
> but I don't know if that can ring any bell....

An update on this issue: it looks like it only happens if "xhci-mtk
11290000.usb" probes before "mtk-pcie-gen3 112f8000.pcie". What they have in
common is that both of those nodes use phys that share the same t-phy block:
pcie uses the usb3 phy while xhci uses the usb2 phy. So it seems that some of
the initialization done by the pcie controller might be implicitly needed by the
usb controller.

This should help to narrow down the issue and find a proper fix for it.

Thanks,
Nícolas