Re: Microchip USB2642 Hub not resuming from USB autosuspend

[Martin Kepplinger <martin.kepplinger@puri.sm>]

On 26.05.20 09:04, Martin Kepplinger wrote:
> hi all,
> 
> our Librem 5 includes the microchip USB2642 hub with
> integrated/connected SD cardcreader (and we connect the baseband modem
> to it): https://www.microchip.com/wwwproducts/en/USB2642
> 
> When we remove the (integrated) SD cardreader entirely (in sysfs), the
> Hub suspends as long as the modem doesn't need a connection. But then
> the modem fails to *resume* the Hub. Linux xhci host times out and dies
> during resuming, which leaves a system without the Hub entirely. You can
> see some logs and tests here
> https://source.puri.sm/Librem5/linux-next/issues/170#note_89808 (when
> scrolling down).
> 
> Microchip says the their product has the following bug which results in
> our problem:
> https://microchipsupport.force.com/s/article/Device-attached-to-Hub-Downstream-Facing-Port-does-not-Resume-from-Suspend
> (that may or may not be the real and only reason for our problem)
> 
> That issue suggests working around it in the HC by somehow
> sending "HS SOF as soon as possible after the HS RESUME EOP".
> 
> We use imx8mq and the dwc3 driver for the designware USB hardware that
> NXP documents in chapter 11.1.3 of the reference manual:
> https://www.nxp.com/products/processors-and-microcontrollers/arm-processors/i-mx-applications-processors/i-mx-8-processors/i-mx-8m-family-armcortex-a53-cortex-m4-audio-voice-video:i.MX8M?tab=Documentation_Tab
> 
> What can we try to change in dwc3 or xhci drivers in order to achieve
> sending SOF earlier after resume?
> 
> What else that I don't currently think of could lead to the USB
> suspend/resume problem here?
> 

Here's what USB traffic is going on when the connected (modem) device
tries to resume the Hub, which fails:

https://source.puri.sm/snippets/382

you can see 1.3.x (SD cardreader) is being removed (manually) for this
test (otherwise the Hub would never suspend). And I marked where I
called the modem in order to resume...

What could I try to change in order to improve my situation and make the
Hub resume?


btw, I'm still trying to get access to the DWC USB3 "programming guide"
that is even reference in the mainline kernel docs:
https://elixir.bootlin.com/linux/latest/source/Documentation/devicetree/bindings/usb/dwc3.txt#L101

thanks,
                              martin