EHCI debugging

Find - USB port on the target that supports EHCI debug
Initial - setup of BBB to act as EHCI debug dongle
Patch - BBB's g_dbgp module (optional, but highly recommended)
Configure - libreboot with EHCI debug -
1. Selecting - HCD Index and USB Debug port
How to get the debug - logs
Eneble - EHCI Debug on the target's kernel (optional, recommended)
References

If your computer does not boot after installing libreboot, it is - very useful to get debug logs from it, from the payload (grub) and/or - the kernel (if gets to there). All of them stream debug logs on the - available serial (RS-232) by default. However, most of todays laptops - lack RS-232 port. The other option is to stream the logs to USB EHCI - debug port.

This section explains step-by-step how to setup BBB as a - “USB EHCI debug dongle” and configure libreboot and the - linux kernel to stream logs to it (TODO: grub).

I will refer to three computers:

host - this is the computer you use, have - tools, compiler, Internet, etc
BBB - Beaglebone Black (rev. B or higher, i - use rev. C)
target - the computer you are trying to - install liberboot

Find USB port - on the target that supports EHCI debug

- Not all USB controllers support EHCI debug (see: EHCI - Debug Port ). Even more, if a USB controller supports EHCI debug, it - is available only on a single port that might or might - not be exposed externally. -

You need running OS (GNU/Linux) on your target for this step - (If you’ve flashed libreboot and it does not boot, you have to - flush back the stock bios)
You need USB memory stick (the data on it will not be - touched).
The EHCI debugging can not be done through external hub, BBB - must be connected directly to the debug port of the controller (so, no - hubs)

Download¹ this - shell script. -

Plug the usb stick in the first available usb port
Run the script, you will get output similar to following:

The following PCI devices support a USB debug port (says lspci): 0000:00:1a.0 0000:00:1d.0
-The following PCI devices support a USB debug port (says the kernel): 0000:00:1a.0 0000:00:1d.0
-*PCI device 0000:00:1a.0, USB bus 3, USB physical port 1*
-*PCI device 0000:00:1d.0, USB bus 4, USB physical port 2*
-Currently connected high-speed devices:
-/:  Bus 04.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/2p, 480M
-	|__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/8p, 480M
-		|__ Port 7: Dev 14, If 0, Class=Hub, Driver=hub/4p, 480M
-			|__ Port 1: Dev 15, If 0, Class=Hub, Driver=hub/4p, 480M
-			|__ Port 3: Dev 17, If 0, Class=Hub, Driver=hub/2p, 480M
-			|__ Port 4: Dev 18, If 0, Class=Hub, Driver=hub/4p, 480M
-/:  Bus 03.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/2p, 480M
-	|__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/6p, 480M
-/:  *Bus 01*.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 480M
-	|__ *Port 3: Dev 31, If 0, Class=Mass Storage, Driver=usb-storage, 480M*
-

The buses the support debug are Bus 3 (0000:00:1a.0) on Port 1 - and Bus 4 (0000:00:1d.0) on port 2. Your usb stick is plugged on Bus - 1, Port 3
Repeat the steps, plugging the USB stick in the next available - port
Go through all available ports and remember(write down) those - for which bus/port of the usb stick matches one of the bus/port that - support debug (bold).

Remember (write down) for each port (external plug) you found - that supports debug: PCI device id, the bus id, the port number, and - the physical location of the usb plug.

If you do not find a match, you can not get debug over EHCI. - Sorry.

- ¹ The guys from coreboot were talking about including the - script in coreboot distribution (check the status). -

Initial setup of - BBB to act as EHCI debug dongle

BBB must be powered with a barrel power connector since the - mini-B USB plug will be used for the EHCI debug stream. So you will - need:

power supply (5V, 2A(10W) is sufficient).
an extra usb cable: A to mini-B

- (On BBB) The linux kernel includes module (g_dbgp that enables one of the usb ports on a computer to behave as EHCI - debug dongle. Make sure you have this module available on your BBB - (Debian 7.8 that comes with BBB should have it), if not, you should - compile it yourself (see next section): -

ls /lib/modules/3.8.13-bone70/kernel/drivers/usb/gadget/g_dbgp.ko

- Unload all other - g_* - modules: -

# lsmod
-# rmmod g_multi
-...
-

- Then load - g_dbgp - : -

# modprobe g_dbgp
-# lsmod # should show that g_dbgp is loaded, and no other g_*
-

- Plug the mini-B side of the USB cable in your BBB and the A side in - your target. Then one of the usb devices on your target (with - lsusb - ) should be: -

Bus 001 Device 024: ID 0525:c0de Netchip Technology, Inc.

If you see the device on the target, you are good to continue to - the next step.

- Patch BBB’s - g_dbgp - module (optional, but highly recommended) -

- For the reasons why you need this, see: EHCI Gadget Debug.
Make - sure that you have cross compiling environment for - arm-linux-gnueabihf - setup on your host. -

On BBB: uname -r - this will give you version - number like 3.8.13-bone70 (I will refer to this as: $mav.$miv-$lv: - where mav=3.8, miv=13, lv=bone70 -
Get the BBB kernel ready on your host for cross-compiling:

$ cd $work_dir
-$ git clone https://github.com/beagleboard/kernel.git
-$ cd kernel
-$ git checkout $mav (see above)
-$ ./patch.sh
-$ wget http://arago-project.org/git/projects/?p=am33x-cm3.git\;a=blob_plain\;f=bin/am335x-pm-firmware.bin\;hb=HEAD -O kernel/firmware/am335x-pm-firmware.bin
-$ cp configs/beaglebone kernel/arch/arm/configs/beaglebone_defconfig
-

Download the patch from here
tar -xf Ehci-debug-gadget-patches.tar.gz (will - create dir: usbdebug-gadget)
Note that there are two patches (patch_1 and patch_2) for each - of the two different version of the kernel (3.8 and 3.10). I will use - 3.8. (If using kernel 3.12 patch_1 is not needed)
cd kernel (note that this is one more level: you - should be in $work_dir/kernel/kernel)
Apply the patches:

-git apply ../usbdebug-gadget/v3.8-debug-gadget/0001-usb-dbgp-gadget-Fix-re-connecting-after-USB-disconne.patch
-git apply ../usbdebug-gadget/v3.8-debug-gadget/0002-usb-serial-gadget-no-TTY-hangup-on-USB-disconnect-WI.patch
-;
-make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- beaglebone_defconfig -j4@
-

- You should also apply the linux-libre deblob script to turn it into linux-libre - (deletes all the blobs from the linux kernel). - fsfla website - - see scripts. -
Get your current BBB kernel config (from: /boot/config-<ver>) - and copy it to your host as $work_dir/kernel/kernel/.config

-make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- oldconfig - all default answers

Set proper version number: -
- On your host, edit $work_dir/kernel/kernel/.config - (the one you’ve just copied from BBB), find the line CONFIG_LOCALVERSION="<something - or empty>" and change it to CONFIG_LOCALVERSION="-$lv", - so it will look something like: CONFIG_LOCALVERSION="-bone70"
-
Also, make sure that: CONFIG_USB_G_DBGP=m (If - not, make menuconfig, and set @Device Drivers-> USB - Support -> USB Gadget Support -> EHCI Debug Device Gadget=m
Build the module:

-$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- -j4 (is it possoble to build only the gadget modules)
-$ mkdir ../tmp && make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- INSTALL_MOD_PATH=../tmp modules_install
-

on BBB, backup /lib/modules/3.8.13-bone70/kernel/drivers/usb/gadget - (i.e. mv - /lib/modules/3.8.13-bone70/kernel/drivers/usb/gadget $HOME) -
copy the freshly compiled usb/gadget dir to /lib/modules/3.8.13-bone70/kernel/drivers/usb
restart BBB
Remove all g_* modules (rmmod - g_<>) -
modprobpe g_dbgp

Configure libreboot with - EHCI debug

- Libreboot(coreboot) should be configured with debug turned on and to - push debug messages to the EHCI debug port.
If you’ve - downloaded the binary distribution, you can check if it is properly - configured in the following way: -

Go to the libreboot dist root directory cd - $libreboot_bin
Locate the rom image for your target (I will call it: $img_path) -
Running the following command will extract the config in a - file ./my_config: -

-./cbfstool/i686/cbfstool $img_path extract -n config -f ./my_config
-

Make sure that the following params in the config are set as - following:

-CONFIG_USBDEBUG=y (Generic Drivers -> USB 2.0 EHCI debug dongle support)
-CONFIG_USBDEBUG_IN_ROMSTAGE=y (Generic Drivers -> Enable early (pre-RAM) usbdebug)
-CONFIG_USBDEBUG_HCD_INDEX=<HCD Index of usb controller - see below> (Generic Drivers -> Index for EHCI controller to use with usbdebug)
-CONFIG_USBDEBUG_DEFAULT_PORT=<USB Debug port - see below> (Generic Drivers -> Default USB port to use as Debug Port)
-

- The following three are behind radio button in the menu. Only the first - one² should be = y -

-USBDEBUG_DONGLE_STD=y                       (Generic Drivers -> Type of dongle (Net20DC or compatible) -> Net20DC or compatible)
-CONFIG_USBDEBUG_DONGLE_BEAGLEBONE=n         (Generic Drivers -> Type of dongle (Net20DC or compatible) -> BeagleBone)
-CONFIG_USBDEBUG_DONGLE_BEAGLEBONE_BLACK=n   (Generic Drivers -> Type of dongle (Net20DC or compatible) -> BeagleBone Black)
-

- ² The g_dbgp module on BeagleBone Black (Rev. C) reports it self as Net20DC, the - other options are for older BB(B) - ver1. This is documented here - (also tested/verified). -

- Then:
-

-CONFIG_CONSOLE_USB=y (Console -> USB dongle console output)
-

- Also - Debugging ---> Output verbose XYZ - ) (FIXME somebody verify these): -

-CONFIG_DEBUG_CBFS=y (Output verbose CBFS debug messages )
-CONFIG_HAVE_DEBUG_RAM_SETUP=y (??? What/where is this)
-CONFIG_DEBUG_RAM_SETUP=y (Output verbose RAM init debug messages)
-CONFIG_DEBUG_SMI=y      (Output verbose SMI debug messages)
-CONFIG_DEBUG_ACPI=y     (Output verbose ACPI debug messages )
-CONFIG_DEBUG_USBDEBUG=y (Output verbose USB 2.0 EHCI debug dongle messages)
-

If some of the above mentioned configuration options are not as - specified, you have to configure and compile libreboot yourself. Please - refer to the doc(FIXME: link about compiling libreboot.

- Selecting - HCD Index - and - USB Debug port -

- This applies (and works) only if the USB controller that supports debug - (found in the first section) is from Intel.
If the PCI ID of the - port you found in the first section is - 0000:00:1a.0 - or - 0000:00:1d.0 - , you are ok. Otherwise you have to try without guarantee that will - work. -

- If the externally exposed port is on a bus with - PCI ID == 0000:00:1a.0 - then for - CONFIG_USBDEBUG_HCD_INDEX - choose 2, otherwise choose 0 - . -

- For - CONFIG_USBDEBUG_DEFAULT_PORT - choose the port from the first section that correspond to the - PCI ID -

- Notes:
The above is based on the implementation of - coreboot/src/southbridge/intel/common/usb_debug.c : pci_ehci_dbg_dev() - .
This is enough as it applies for the supported GM45/G45 - Thinkpads. coreboot support some other contollers too, but they are - irellevent for libreboot (for now). -

On T500 (with switchable GPU) the debug ports for both intel - controllers is exposed.
On x200t the debug ports for both intel controllers is - exposed.

How to get the debug logs

Plug the USB cable in the target’s debug port (the one - you found in step 1) and BBB’s mini-B USB
Make sure no other then g_dbgp of the g_* - modules is loaded on your BBB -
On the BBB:

-stty -icrnl -inlcr -F /dev/ttyGS0
-cat /dev/ttyGS0
-

Power on the target with libreboot
You should see debug logs comming on your BBB console

- Note that this is not permanent on BBB, if you reboot it, you have to - rmmod g_* - and - modprobe g_dbgp -

Eneble - EHCI Debug on the target’s kernel (optional, recommended)

You have to know how to compile kernel for your target.

Check if early debugging is already enabled: grep - CONFIG_EARLY_PRINTK_DBGP /boot/config-<ver>
If enabled, you do not have to compile the kernel (skip this - step). Otherwise, prepare kernel source for your distribution and - select (Kernel hacking -> Early printk via EHCI debug - port). Compile and install the new kernel. -
Edit your grub configuration and add following to the kenel - parameters²⁰²¹: earlyprintk=dbgp,keep. - Also, try: earlyprintk=dbgp<N>,keep where N - is the debug port id if the first does not work. -

References

- ¹⁰ EHCI - Debug Port -

- ¹¹ coreboot - EHCI debug gadget demonstration -

- ¹² EHCI - Gadget Debug -

- ¹³ Ehci-debug-gadget-patches.tar.gz -

- ¹⁴ Compiling - the BeagleBone Black Kernel -

- ¹⁵ - http://dumb-looks-free.blogspot.ca/2014/06/beaglebone-black-bbb-compile-kernel.html -

- ¹⁶ - http://dumb-looks-free.blogspot.fr/2014/06/beaglebone-black-bbb-kernal-headers.html -

- ¹⁷ Building - BBB Kernel -

- ¹⁸ - http://komposter.com.ua/documents/USB-2.0-Debug-Port%28John-Keys%29.pdf -

- ¹⁹ Exploring - USB at the Hardware/Software Interface -

- ²⁰ - https://www.kernel.org/doc/Documentation/x86/earlyprintk.txt -

- ²¹ https://wiki.ubuntu.com/Kernel/Debugging/USBearlyprintk -

- TODO: -

grub does not send messages to EHCI debug. Investigate.
The section “Configure libreboot with EHCI debug” - can be skipped/simplified if a common configuration works for all - relevant targets is selected as defualt
Patch and compule g_dbgp on BBB instead cross-compile
Find a simple way to send debug messages from targets userland

EHCI debugging on the BeagleBone Black