Error message
xillybus: Failed to quiesce the device on exit. Quitting while leaving a mess.Meaning
This fatal error is issued when the Xillybus host driver fails to stop all activity on the FPGA side, which is one of the steps in unloading the driver from the Linux kernel. This effectively means that the driver is declared as unloaded by the Linux kernel, but its resources are partially not freed. For example, as the RAM buffers are accessed by the FPGA through DMA, this memory is not freed, since there is no confirmation from the FPGA that they will not be accessed anymore.
This condition is normal when the FPGA has been reconfigured since the driver was loaded into the Linux kernel, or otherwise made unresponsive.
Recommended action
To get Xillybus working again, power the computer off, reconfigure the FPGA and power the computer on again.