Re: dwc3 inconsistent gadget connection state?

[Felipe Balbi <balbi@kernel.org>]

[-- Attachment #1: Type: text/plain, Size: 2905 bytes --]


Hi,

John Stultz <john.stultz@linaro.org> writes:
>   I've been tripping over an issue on my HiKey960 where with the usb-c
> gadget cable connected, the gadget code doesn't consistently seem to
> initialize properly. I had rarely seen this behavior previously, but
> more recently it has become more frequent and annoying.
>
> Usually, unplugging and replugging the USB-C cable would get things
> working again (but that's not helpful in test labs).
>
> I annotated a bunch of code trying to understand what was going on and
> I narrowed down the difference in the good and bad case to a dwc3
> reset interrupts happening after usb_gadget_probe_driver() completes.
> In the good case, we see the reset interrupts, and in the failed case
> we don't.
>
> [   16.491953] JDB: usb_gadget_probe_driver
> [   16.495938] JDB: udc_bind_to_driver
> [   16.499555] JDB: dwc3_gadget_start irq: 65 revision: 1429417994
> [   16.503803] JDB: __dwc3_gadget_ep_enable
> [   16.507791] JDB: __dwc3_gadget_ep_enable
> [   16.511715] JDB: dwc3_gadget_enable_irq
> [   16.515582] JDB: usb_udc_connect_control
> [   16.519510] JDB: usb_gadget_connect
> <in the bad case, this is all we see, the gadget device doesn't come up>
> [   16.811010] JDB: dwc3_gadget_interrupt
> [   16.814783] JDB: dwc3_gadget_reset_interrupt
> [   16.819047] JDB: dwc3_reset_gadget
> [   16.823935] JDB: dwc3_gadget_interrupt
> [   16.827686] JDB: __dwc3_gadget_ep_enable
> [   16.831611] JDB: __dwc3_gadget_ep_enable
> [   16.994477] JDB: dwc3_gadget_interrupt
> [   16.998246] JDB: dwc3_gadget_reset_interrupt
> [   17.002519] JDB: dwc3_reset_gadget
> [   17.005922] JDB: usb_gadget_udc_reset
> [   17.062422] JDB: usb_gadget_set_state  state: 5
> [   17.067069] JDB: dwc3_gadget_interrupt
> [   17.070823] JDB: __dwc3_gadget_ep_enable
> [   17.074745] JDB: __dwc3_gadget_ep_enable
> [   17.170898] JDB: usb_gadget_set_state  state: 6
> [   17.195605] JDB: usb_gadget_set_state  state: 7
> [   17.200179] JDB: __dwc3_gadget_ep_enable
> [   17.204118] JDB: __dwc3_gadget_ep_enable
> [   17.208057] JDB: usb_gadget_vbus_draw
> [   17.211721] JDB: usb_gadget_set_state  state: 7
> <in the good case everything is happy here>
>
>
> This sounds a bit like the issue in the comment here:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/usb/dwc3/gadget.c?h=v5.8-rc3#n3143
>
> However, I've tried calling dwc3_gadget_reset_interrupt() and
> dwc3_reset_gadget() at the tail end of dwc3_gadget_start() but that
> doesn't seem to help.
>
> I was curious if you or anyone else had any thoughts on how to debug
> this further?

Try enabling dwc3 tracepoints and collecting working and failing
cases. If I were to guess, I would say there's a small race condition
between setting pullup and the transceiver sending the VBUS_VALID signal
to dwc3.

-- 
balbi

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 832 bytes --]