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