Seems I am reaching one of my goals of my original GSoC proposal in bringing usbdebug available as a compile option for most the mainboards with compatible chipset.
As I wrote in an earlier blog, it has been more of a refactoring job on existing code rather than creating something entirely new. There are a series of protocol details where I spotted the implementation took some shortcuts and I have attempted to fix those. I also made improvements to better control how the possible debug dongle connection is probed. There is more testing needed there and also it needs to be fixed to not become excessively slow when dongle is not connected or if it is disconnected before OS is loaded.
At the time of writing, my patches have not yet been submitted to master but are available on the gerrit review board. It is likely there will be some minor fixes, so I will not give exact commit hashes one should checkout and merge. In short: checkout and merge the two topic-branches usbdebug-cfg and usbdebug-lib. In addition, for AMD Agesa boards one needs “AMD AGESA: Place CAR_GLOBAL in BSP stack”.
Now if you only had something to connect it with, I could ask for your help actually testing these changes and finding out if it works! I am still waiting for my BeagleBone Black to arrive to make some fixes to the kernel EHCI debug gadget driver, and the situation with the choice of debug dongles will then improve quite radically. I do have the older BeagleBone and have built custom kernel modules for it and I have started to study how g_dbgp driver interacts with the gadget serial port framework.
What I discovered after picking up a second-hand original BeagleBone was that it does not have its USB port directly connected to the ARM chip, but there is an USB hub chip in between. It might be possible to configure that hub even though our USB requests are limited to a length of max 8 bytes per transaction. The EHCI debug specs do not allow a hub there, but if we can make it work, why not do it?