On Wed, Dec 19, 2018 at 8:54 AM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Wed, Dec 19, 2018 at 08:41:56AM +0200, Ranran wrote: > > On Wed, Dec 19, 2018 at 12:00 AM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > 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. > > > > > > > We have strict demands of boot time for up to 2-3 seconds. > > Boot time to what exactly? And again, have you tested your system? > > USB devices probe asynchronously, other things will happen while they > are being discovered. > > > We have a usb touch screen, and some of us think that usb enumeration > > is problematic (in terms of boot time) and that we better change the > > initerface t touch screen from usb to serial. > > Have you tested this? You need to do that. > > > Please tell me what you think, is it really better to change the > > interface or can we speed up the usb enumeration of this device ? Will > > it get into the 2-3 seconds limitation ? > > Again, you need to test this for your hardware. We have no idea what > exactly you are using, nor can we give you any firm answers. You need > to do that testing yourself. > I understand. I shall do it. How can we measure enumeration time of usb ? and is there a way to speedup the enumeration time ? We have single usb known device, and don't use other usb devices.. Thank you very much, ran > good luck! > > greg k-h
