linux-kernel - Re: earlyprintk=xdbc seems broken

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Date:   Fri, 3 Dec 2021 08:52:53 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc:     baolu.lu@...ux.intel.com, x86@...nel.org,
        linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
        linux-usb@...r.kernel.org
Subject: Re: earlyprintk=xdbc seems broken

Hi Peter,

On 12/2/21 11:22 PM, Peter Zijlstra wrote:
> Hi Lu,
> 
> I was unfortunate enough to need xdbc and can't get my machine to boot
> with earlyprintk=xdbc on the cmdline.
> 
> When I boot the target without the earlyprintk=xdbc, but have the cable
> attached, it won't boot because boot gets stuck like:
> 
> Dec  2 15:08:10 tigerlake kernel: [   42.043137] usb usb4-port3: Cannot enable. Maybe the USB cable is bad?
> Dec  2 15:08:10 tigerlake kernel: [   42.043227] usb usb4-port3: config error
> 
> However, when I boot without earlyprintk=xdbc, without the cable
> attached, then I can attach the cable and:
> 
> $ echo enable > /sys/bus/pci/devices/0000:00:14.0/dbc
> 
> will actually work, and it shows up on my host system:
> 
> [1023855.419430] usb usb2-port3: Cannot enable. Maybe the USB cable is bad?
> [1023855.419455] usb usb2-port3: config error
> [1023859.491476] usb usb2-port3: Cannot enable. Maybe the USB cable is bad?
> [1023859.491487] usb usb2-port3: config error
> [1023861.335436] usb usb2-port3: config error
> [1023861.607476] usb 2-3: new SuperSpeed USB device number 7 using xhci_hcd
> [1023861.627614] usb 2-3: LPM exit latency is zeroed, disabling LPM.
> [1023861.627853] usb 2-3: New USB device found, idVendor=1d6b, idProduct=0010, bcdDevice= 0.10
> [1023861.627855] usb 2-3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
> [1023861.627856] usb 2-3: Product: Linux USB Debug Target
> [1023861.627857] usb 2-3: Manufacturer: Linux Foundation
> [1023861.627858] usb 2-3: SerialNumber: 0001
> [1023861.629344] usb_debug 2-3:1.0: xhci_dbc converter detected
> [1023861.629532] usb 2-3: xhci_dbc converter now attached to ttyUSB0
> 
> 
> Can you please see if you can repro and fix this?
> 
> This all was with current 5.16-rc3 on a tigerlake nuc.
> 
> Also, perhaps you can update the guide on what sort of setup/cables
> etc.. you need when either the host or the client is a usb3.1 usb-c only
> device.
> 

+ Mathias, maybe he still has a USB 3.0 debugging cable.

Best regards,
baolu