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From:   Mathias Nyman <mathias.nyman@linux.intel.com>
Subject: Re: earlyprintk=xdbc seems broken
Message-ID: <dfb311e3-1a83-31a2-3c82-fd982c0757f6@linux.intel.com>
Date:   Mon, 24 Jan 2022 16:55:22 +0200
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> [    0.000000] xhci_dbc:early_xdbc_parse_parameter: dbgp_num: 0
> [    4.984106] xhci_dbc:xdbc_start: waiting for connection timed out, DCPORTSC:0xa0
> [    9.946159] xhci_dbc:xdbc_start: waiting for connection timed out, DCPORTSC:0xa0
> [    9.946163] xhci_dbc:early_xdbc_setup_hardware: failed to setup the connection to host
>
> [   12.818364] xhci_hcd 0000:00:0d.0: xHCI Host Controller
> [   12.818373] xhci_hcd 0000:00:0d.0: new USB bus registered, assigned bus number 1
> [   12.820360] xhci_hcd 0000:00:0d.0: xHCI Host Controller
> [   12.820363] xhci_hcd 0000:00:0d.0: new USB bus registered, assigned bus number 2
> [   12.821036] xhci_hcd 0000:00:14.0: xHCI Host Controller
> [   12.821040] xhci_hcd 0000:00:14.0: new USB bus registered, assigned bus number 3
> [   12.823451] xhci_hcd 0000:00:14.0: xHCI Host Controller
> [   12.823453] xhci_hcd 0000:00:14.0: new USB bus registered, assigned bus number 4
> [   17.115089] usb usb4-port4: Cannot enable. Maybe the USB cable is bad?
> [   17.115163] usb usb4-port4: config error

Ok, I see it now.
Your setup has two xhci controllers, earlypringk=dbc enables dbc on the first xhci
it finds, which would be at 0000:00:0d.0.
Your cable is connected to the second xhci host at 0000:00:14.0

does using "earlyprintk=xdbc1" work?

Thanks
-Mathias