On Tue, 18 Dec 2018, Ranran wrote: > Hello, > > We are afraid that the USB enumeration might take too much time (~3 > seconds) , and consider to disable usb and change interface to device > from usb to serial. > > Does anyone knows if it usb enumeration really takes that long in > recent kernels ? USB enumeration time doesn't depend much on the kernel version, but it does depend on what USB devices are connected and lots of other things, such as how busy the system is. The best way to find out how long it takes on your system is to measure it. > Is it that usb enumeration at startup can be postponed ? If you build the USB controller drivers as modules and prevent those modules from being loaded at boot time (for example, by moving them into a directory different from where they normally belong) then no USB enumeration will take place at startup. Some time later you can load the modules manually, and enumeration will begin. But I have to admit, it's hard to see why you would want to postpone enumeration if you're worried that it will take too long. I should think you'd be more interested in speeding it up than delaying it. Alan Stern
