Subject: Re: [PATCH v3 00/12] usb: early: add support for early printk through
 USB3 debug port
To: Dave Young <dyoung@redhat.com>
References: <1447054721-7390-1-git-send-email-baolu.lu@linux.intel.com>
 <20151110093934.GB22332@localhost.localdomain>
Cc: Mathias Nyman <mathias.nyman@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Alan Stern <stern@rowland.harvard.edu>, linux-usb@vger.kernel.org,
        x86@kernel.org, linux-kernel@vger.kernel.org
From: "Lu, Baolu" <baolu.lu@linux.intel.com>
Message-ID: <56429ABF.4020802@linux.intel.com>
Date: Wed, 11 Nov 2015 09:32:47 +0800
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On 11/10/2015 05:39 PM, Dave Young wrote:
> Hi,
>
> On 11/09/15 at 03:38pm, Lu Baolu wrote:
>> This patch series adds support for early printk through USB3 debug port.
>> USB3 debug port is described in xHCI specification as an optional extended
>> capability.
>>
> I did a test with your previous patchset with the manually wired cable.
> debug host detected the remote device, but later the devie automaticlly
> disconnected and earlyprintk hangs.

Hi Dave,

What I have done is:

(1) Build a new kernel for debug target with this patch series applied.
(2) Add "earlyprintk=xdbc" to the kernel option of debug target. The
      "keep" option for early printk doesn't support yet. (That's my next
      target.)

(3) Boot the debug host, and disable USB runtime suspend:

# echo on > /sys/bus/pci/devices/<xhci_pci_bus_name>/power/control
# echo on | tee /sys/bus/usb/devices/*/power/control

(4) Boot the debug target. Check the dmesg message on debug host.

# tail -f /var/log/kern.log

Nov 12 01:27:50 allen-ult kernel: [ 1815.983374] usb 4-3: new SuperSpeed 
USB device number 4 using xhci_hcd
Nov 12 01:27:50 allen-ult kernel: [ 1815.999595] usb 4-3: LPM exit 
latency is zeroed, disabling LPM.
Nov 12 01:27:50 allen-ult kernel: [ 1815.999899] usb 4-3: New USB device 
found, idVendor=1d6b, idProduct=0004
Nov 12 01:27:50 allen-ult kernel: [ 1815.999902] usb 4-3: New USB device 
strings: Mfr=1, Product=2, SerialNumber=3
Nov 12 01:27:50 allen-ult kernel: [ 1815.999903] usb 4-3: Product: 
Remote GDB
Nov 12 01:27:50 allen-ult kernel: [ 1815.999904] usb 4-3: Manufacturer: 
Linux
Nov 12 01:27:50 allen-ult kernel: [ 1815.999905] usb 4-3: SerialNumber: 0001
Nov 12 01:27:50 allen-ult kernel: [ 1816.000240] usb_debug 4-3:1.0: 
xhci_dbc converter detected
Nov 12 01:27:50 allen-ult kernel: [ 1816.000360] usb 4-3: xhci_dbc 
converter now attached to ttyUSB0

(5) Host has completed enumeration of debug device. Start "minicom" on 
debug host.


Welcome to minicom 2.7

OPTIONS: I18n
Compiled on Jan  1 2014, 17:13:19.
Port /dev/ttyUSB0, 01:28:02

Press CTRL-A Z for help on special keys

Press Y to continue...

(6) You should be able to see "Press Y to continue..." (if not, try 
pressing Enter key)
Press Y key, debug target should go ahead with boot and early boot 
messages should show in mincom.

Press Y to continue...
[    0.000000] Initializing cgroup subsys cpuset
[    0.000000] Initializing cgroup subsys cpu
[    0.000000] Initializing cgroup subsys cpuacct
[    0.000000] Linux version 4.3.0-rc7+ (allen@blu-skl) (gcc version 
4.8.4 (Ubuntu 4.8.4-2ubuntu1~14.04) 5
[    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-4.3.0-rc7+ 
root=UUID=5a2fb856-0238-4b6e-aa45-beeccb7
[    0.000000] KERNEL supported cpus:

[...skipped...]

[    0.000000]  Offload RCU callbacks from CPUs: 0-7.
[    0.000000] Console: colour dummy device 80x25
[    0.000000] console [tty0] enabled
[    0.000000] bootconsole [earlyxdbc0] disabled


So "the devie automaticlly disconnected and earlyprintk hangs" happens 
in which step?

Thanks,
Baolu

>
> I have not got more time, will try your new patchset when I have time.
>
> Thanks
> Dave
>

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