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

[AngeloGioacchino Del Regno]

Il 10/07/24 21:15, Nícolas F. R. A. Prado ha scritto:
> 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@mediatek.com/
>>> [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.
> 

This gave me a couple ideas to try... and it looks like I have resolved this issue.

A commit will follow soon.

Thank you!
Angelo