对于Ubuntu16.04中jstest-gtk不能正常识别Logitech G920 racing wheel的问题补充
在之前的一篇文章里面，留下的问题是不能完美解决jstest-gtk不能正常识别Logitech G920方向盘的问题。
虽然可以通过重启电脑到windows下进行设置一番，但是始终没有彻底解决jstest-gtk正常识别方向盘的问题。
现在，我通过查资料，逛Github，知道了原因，但是才疏学浅，根据大神的教程，始终未能彻底解决jstest-gtk识别方向盘的问题。这里我附上了原因以及解决问题的教程，望共勉，希望有才之士解决的话分享一下经验，多谢。
在ubuntu系统终端输入lsusb，对于方向盘显示的0xc261与0xc262，是由于方向盘自动默认启动Xbox模式，需要修改模式，安装并启用usb_modeswitch。
参考链接：
1、https://lkml.org/lkml/2016/1/26/763
2、http://www.draisberghof.de/usb_modeswitch/bb/viewtopic.php?f=2&t=2510
3、http://www.draisberghof.de/usb_modeswitch/
4、http://burning-midnight.blogspot.com/2017/11/logitech-g920-steering-wheel-on-linux.html （需要梯子）
5、https://github.com/carla-simulator/carla/issues/1473
问题：
参照这几篇教程，虽然知道是什么原因导致Ubuntu读不出来方向盘，还是没有弄懂如何添加命令行修改参数。虽然是可以成功地解决jstest-gtk识别方向盘的问题。
附上第四条链接的内容：
Logitech G920 Steering Wheel on Linux - Ubuntu 16.04, Linux Mint 18
Yes, it works. And...well, it's not terrible to make it work, but it was a bitch to find all the missing pieces.
For the search engines... think Euro Truck Simulator 2. Linux. Ubuntu and Mint. This information won't be relevant for too much longer, but for my own sanity I'm writing it down anyway.
For starters, Ubuntu 17 already has the necessary changes to the UDEV rules file. Mint 18 is based on Ubuntu 16, so you're stuck there without the following.
Upgrading the Kernel Version
Kernel series 4.4 does not have the necessary improvements to the hid_logitech_hidpp.ko module. The 4.8 and later series kernels (supposedly also 4.6) have it. Check Linus' kernel git and locate the module source if you want to enjoy a front-row seat in the time-machine. I pushed my Mint 18 install to 4.10, partly for kicks; I figured it was a good compromise between new and working, although I have virtually no other experience and can't say what else might be fixed/broken over the 4.4 kernel that my Mint install was running...
Now, if you have a clean install of Mint, it might already be on a newer release. My work computer was on 4.8; I had done upgrades to my home PC, however, and so the kernel version seemed to lag. USE THE UPDATE MANAGER TO SELECT A NEW KERNEL VERSION!
References: http://linuxbsdos.com/2016/12/19/how-to-upgrade-the-kernel-in-linux-mint-18-1-from-4-4-to-4-8/
Also be careful /boot doesn't run out of space. That is very annoying.
Once you have the newest kernel installed, you can move on to the UDEV system and the usb_modeswitch updates.
UDEV and usb_modeswitch
It's probably a good idea to start with the usb_modeswitch. Again, newer versions of Ubuntu have this fix already loaded. You'll need to create a file in /etc/usb_modeswitch.d/ called "046d:c261". Inside, dump the following:
# Logitech G920 Racing Wheel
DefaultVendor=046d
DefaultProduct=c261
MessageEndpoint=01
ResponseEndpoint=01
TargetClass=0x03
MessageContent="0f00010142"
The next step is to insert the following rule into udev. I stuffed mine into the rules file: /lib/udev/rules.d/40-usb_modeswitch.rules, however you might want to try using the /etc/udev/rules.d/ folder instead. If the latter doesn't work, the former certainly does...you just run the slight risk of future upgrades wreaking havoc when they get to this file.
ATTR{idVendor}=="046d", ATTR{idProduct}=="c261", RUN+="usb_modeswitch '%b/%k'"
References: http://www.draisberghof.de/usb_modeswitch/bb/viewtopic.php?f=2&t=2510
Why is this necessary?
As explained in the latter link, the steering wheel powers up in XBOX mode. A command must be sent to switch the wheel over to PC mode, or there is no PC goodness. usb_modeswitch does this.
Hazards
On these "older" versions of Ubuntu (ahem...Mint), you might run into a problem with usb_modeswitch if you're using USB hubs. Evidently the older versions of usb_modeswitch might have trouble dealing with cascaded hubs, which could explain why I was able to get this to work on my Mint PC (a laptop I plugged directly into) and not my Xubuntu desktop (where I plugged into my USB KVM switch). Newer versions of usb_modeswitch, such as that which ships with Ubuntu 17, supposedly do not suffer from this deficiency. Now, I state this only to help debug, I haven't verified it, and YMMV. Every time I pull out the steering wheel, I have to do it under cover of closed and locked door because it's a gift for my son (yeah, the kids get all the cool toys).
Also, you CAN actually get the wheel talking to Ubuntu/Mint without the newer kernel, BUT THE FORCE-FEEDBACK WILL NOT WORK! That component is contingent on the kernel module, and if it doesn't talk to the G920, then you will have nothing more than a very expensive set of potentiometers. That said, it is reassuring that to find that your wheel IS appearing to the system as a valid device of some sort, just to let you know that you're on the right track. You'll also note that the incorrect version of the kernel module will not auto-load; the correct version will. Watch lsmod and grep on "hid" to see the action.
Euro Truck Simulator 2!!!!!!
On my laptop, which is technically a work laptop, I have a shitty Intel graphics chipset, so ETS2 ran basically without textures. So that's what that looks like.... But it ran enough to let me test the wheel and get everything working without borking my wife's (significantly better) system. (Yeah, the tech guy who makes old hardware work for a long time suffers with old hardware for a long time...). Once the correct kernel module was loaded, and the udev rules were in place, I watched the syslog and observed the correct initialization sequence via usb_modeswitch occurring. On to ETS2, and enable force-feedback, and HOLY DAMN! Engine rumble, dampening, response... I even crashed on purpose to see how it would feel. Everything was solid gold.
Torcs gives some minor feedback also; I don't know much about configuring it, though, so I suppose it could be better. If anyone else has Linux racing sims they'd like to share, that support wheels and force-feedback, I'm all ears! Never thought I'd honestly buy one of these, but with the newer kernels, it is definitely a good buy.
A Side Note: the Brake Pedal
There are reports that the G29 and G920 both suffer from Logitech trying to, *cough* improve *couch* their brake pedal by inserting a rather rigid piece of rubber into the spring. You have three choices, two of which involve voiding the 1 year warranty (and mine is already like 6 months gone because the damn things has been sitting in a closet after I bought it on sale)...
- Do nothing (and keep your warranty...and possibly suffer with a very stiff brake)
- Open the device and remove the rubber insert - this reportedly returns the unit to G27 performance.
- Open the device and replace the springs with a SPRING UPGRADE!!! I totally want to do this...
This set looks pretty cool, and the reviews I have seen tend to be very positive:
http://www.gteye.com.au/product/gteye-complete-pedal-spring-set-for-logitech-g25-g27
The set works in the G920, and now all I need to do is to talk my wife into letting me buy it...um...for my son's steering wheel and pedal set.... ;-)