I have a new machine (AMD 3960X with a MSI motherboard). I have 4 separate drives with different OS's (Ubuntu 20.04, Windows 10 and 2 versions of Ubuntu 16.04). I keep then completely independent on separate physical drives. I use Ubuntu 20.04 as my primary boot device (the one that Grub runs from). When I boot, I have no keyboard access, so it boots to the most recent usd OS. The workaround to change OS's is the when I am in the Grub boot menu (i.e. for 10 seconds), if I plug a USB pen drive into a USB port, the keyboard starts working. Unplugging and re-plugging in either the mouse or keyboard doesn't work. There is something about plugging in a USB drive that causes the USB ports to be reset, or something similar.
I have seen this problem in the past, and the fix has always been bios settings to enable legacy devices and disable hand-off. This doesn't work. There are no USB2.0 ports on the motherboard, only USB3.x. I have also tried preloading various modules in grub (usb, usb_keyboard, usbms, usbtest). None of them make any difference.
I don't think it has anything to do with Ubuntu versions (16.04 does the same). I think it is a problem that grub has with recent hardware. Has anyone else seen this problem and have a fix?
Answers
To solve this problem I updated the bios from v2.00 to v2.50 but I don't think that made any difference. With the newer bios, I found that if I pressed a key (I used the escape key) just after the numlock light comes on, but before the post beep then the keyboard usually works in Grub. There is some timing with the keypress, but I got used to it fairly quickly. If you press the key after the post boot then the keyboard won't work until the OS boots up. It's not the best solution, but it's better than plugging and unplugging a USB key. I think the keypress causes the USB device to be used so it initializes correctly.
I am posting this so that anyone with a similar problem will know where to look.
The motherboard is a MSI TRX40 Pro Wifi, but I suspect it isn't specific to this brand or this model. The CPU is a AMD 3960X.
