Since I cannot add my findings as a comment, I'll add it as an answer.
My setup: ASRock Z97 Extreme6 and Ubuntu 15.10
What I found out so far:
It seems related to Z97 & similar chipsets: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1437492
Solutions mentioned there are:
- Power off, pull the plug & wait a bit, then power on again -> works for one boot sequence
- Disable Asmedia controller / Asmedia USB controller or similar. These seem to be located in different spots depending on the board. I found 2 potential matches.
Advanced -> USB Configuration -> Third Party USB 3.0 Controller and
Advanced -> Storage Configuration -> 'ASMedia SATA3 Mode'
So what I tried:
- I began from a clean Config (Fresh after CMOS reset)
- The ASMedia setting in "Storage Configuration" I have tried in the past -> this disables some of the SATA ports, so I tried a different route first.
- Go to
Advanced -> USB Configuration -> Set 'Third Party Controller' to Disabled Result: Boot sequence is still slow, but Ubuntu is back to normal speed. Well, my mouse did not work anymore (I had to switch to a different tty to reboot my computer...). Back to UEFI setup.
- Go to
Advanced -> USB Configuration -> Set 'Intel USB3.0 Mode' from 'Smart Auto' to 'Enabled' Result: Scratch that, did not help. Only the front panel USBs work...
- Next I tried shutting down, cut the power for a few minutes, then boot again. Result: That did the trick. System boot time was just a few seconds total. And the USB ports on the back of my computer work again, too.
- Next: verify by rebooting again. Result: Yep, still working.
- Another update: Well, most of the ports work.. Some still don't work. But since I use a hub I can live with that for now. If you try it, maybe the power off & cut power is enough? Might be worth a try..
I'm not sure if all changes above are required - but it is working for me now, so I won't touch these again ;)
I hope this helps you & potentially other people stumbling across the same issue. I also recommend reading the launchpad bug linked above -> That bug report is worth it's weight in gold!
Below are some failed attempts messing with the Legacy Mode settings, that did not solve my problem. Summary: Legacy modes, Compatibility patches, etc. don't really improve the situation, they mostly just randomly disable your devices.. They might help others, so I leave them here for reference.
Playing around with some settings I have found out the following:
Note that I tried to set the USB 2.0 Legacy support to "UEFI Setup Only" so I could get into the setup by plugging the keyboard into the 2.0 ports on my front panel, just to be sure. That did NOT work. These ports are pretty much usesless & my keyboards only work when plugged into a port with legacy support enabled, OR into the hub on my monitor. Any, of yourse, only once Ubuntu started up. Neither UEFI nor Grub would recognize the keyboard. Another keyboard I could get to work on one of the 2.0 ports, so I could get around a CMOS reset.
With "USB Compatibility Patch" enabled:
When plugged directly into the USB 3.0 Ports on the Motherboard, they only work when I enabled USB 3.0 Legcy support in the UEFI setup. When I do that, boot sequence is ~20 seconds longer than the usual 1-3 seconds. Ubuntu then also takes longer to start up, with the
device descriptor read/all, error -110 errors, as displayed above. The keyboard works, but the USB camera I have (Logitech QuickCam Communicate STX, pretty old..) is not recognized by the system.
When the legacy mode is disabled but the two devices are plugged into the hub on my monitor (powered hub, I guess), boot sequence is blazingly fast if no device is plugged into the 2.0 ports BUT Ubuntu still takes longer & displays these messages. Both keyboard and camera work.
Legacy Mode enabled, pretty much yields the same result.
With "USB Compatibility Patch" disabled:
Same behaviour as above, but the other keyboard on the 2.0 Port did not work either... --> CMOS reset.
I'll experiment some more and update this answer as I gather results.