Re: [PATCH 4/8] usb: dwc3: qcom: fix runtime PM wakeup

[Matthias Kaehlcke <mka@chromium.org>]

On Thu, Aug 04, 2022 at 06:04:53PM +0200, Johan Hovold wrote:
> On Thu, Aug 04, 2022 at 08:35:10AM -0700, Matthias Kaehlcke wrote:
> > On Thu, Aug 04, 2022 at 09:35:16AM +0200, Johan Hovold wrote:
> 
> > After enabling runtime suspend for the dwc3 core, dwc3 glue and the xHCI
> > the dwc3-qcom enters autosuspend when the delay expires.
> > 
> > > And the controller is resumed in the wakeup-interrupt handler for the
> > > runtime PM case.
> > >
> > > It seems to work ok, and it looks like the driver has supported this
> > > since it was first merged.
> > 
> > With and without your patch dwc3-qcom enters autosuspend and stays there.
> > USB devices like a mouse or a USB to Ethernet adapter keep working while
> > the glue is suspended.
> 
> Are you sure you're looking at the right controller? And that it is
> actually suspended?

Good point! My mind was set on a SC7180 system, which has a single dwc3
controller, but this time I was tinkering on a SC7280 board, which has
two dwc3, and obviously I was looking at the wrong one (－‸ლ)

> If you plug in a keyboard, enable autosuspend for all devices in the
> path (from glue to the keyboard device) and type away, then the
> controller must remain active. Stop typing, and all devices in the chain
> should suspend.

That's what I expected, and now that I'm looking at the right controller
I'm seeing it. I wondered whether the glue device was somehow special.

> > How is the runtime resume triggered for the dwc3 glue?
> 
> Either by the host driver when it needs to access the device, or by the
> device if it is remote-wakeup capable (e.g. a keyboard, but not
> necessarily a speaker).
> 
> Note that the latter part is what is broken currently as the wakeup
> interrupts were not enabled and those are needed to wake up sc8280xp 
> when the dwc3 glue has been runtime suspended.

Thanks for helping me to get a better understanding!