Re: [PATCH v3 00/12] usb: early: add support for early printk through USB3 debug port
From: Lu, Baolu
Date: Tue Nov 10 2015 - 20:33:01 EST
On 11/10/2015 05:39 PM, Dave Young wrote:
On 11/09/15 at 03:38pm, Lu Baolu wrote:
This patch series adds support for early printk through USB3 debug port.
I did a test with your previous patchset with the manually wired cable.
USB3 debug port is described in xHCI specification as an optional extended
debug host detected the remote device, but later the devie automaticlly
disconnected and earlyprintk hangs.
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
(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:
Nov 12 01:27:50 allen-ult kernel: [ 1815.999904] usb 4-3: Manufacturer:
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
Welcome to minicom 2.7
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+
[ 0.000000] KERNEL supported cpus:
[ 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?
I have not got more time, will try your new patchset when I have time.
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