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From:   Rajaram R <rajaram.officemail@gmail.com>
Date:   Wed, 26 Jan 2022 01:09:49 +0530
Message-ID: <CAOiXhaJPvs5hx_7wFyTm=npvojcF4WOGdnTACSgCOAvJD86i7w@mail.gmail.com>
Subject: Re: earlyprintk=xdbc seems broken
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Mathias Nyman <mathias.nyman@linux.intel.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Lu Baolu <baolu.lu@linux.intel.com>, x86@kernel.org,
        LKML <linux-kernel@vger.kernel.org>, linux-usb@vger.kernel.org,
        Chunfeng Yun <chunfeng.yun@mediatek.com>
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On Wed, Jan 26, 2022 at 12:11 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> 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' ?

I have used DbC with USB-C to A and it works