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Date:   Tue, 25 Jan 2022 13:45:50 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Mathias Nyman <mathias.nyman@linux.intel.com>
Cc:     Greg KH <gregkh@linuxfoundation.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Lu Baolu <baolu.lu@linux.intel.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
        Chunfeng Yun <chunfeng.yun@mediatek.com>
Subject: Re: earlyprintk=xdbc seems broken
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On Mon, Jan 24, 2022 at 04:55:22PM +0200, Mathias Nyman wrote:
>  
> > [    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

I suspect the first xhci controller is for the usb-c ports on the
machine, while the second one has the usb-a ports covered.

Now the documentation states we need this super speed A<->A cable, but
could you also update the documentation for usb-c ? There's a fair
number of usb-c only devices out there now.

C<->A and C<->C cables are fairly easy to come by, would they 'just
work' ?