On Sat, 9 Apr 2016, Sam Sany wrote: > Hi Allen, thank you for quick reply. It is VERY much appreciated. > > The output of /sys/kernel/debug/usb/devices can be found here: > http://pastebin.com/HyzefGyB > (I believe the relevent portion is at the end, the "Focusrite Scarlett" > device). It looks quite normal, except for the fact that there are two copies of everything (which shouldn't hurt). Somebody else reported a similar problem not long ago. It turned out to be caused by a problem with the xHCI controller involving Link Power Management -- disabling LPM fixed it. However, the 4.2 kernel does not have any way to disable LPM (4.5 does). > According to the output of "cat /boot/config" the CONFIG_USB_XHCI_HCD is > modulaized. So can I simply "modprobe -r" it like any module? You can, but I don't think it will help. > I have yet to try the 4.5 kernel. I prefer to use a low-latency kernel, bc > the primary purpose of this machine is recording music. So I have been > downloading the newest source code available in the Ubuntu Studio > repositories, configuring with the xhci drivers modulized (by default Ubuntu > makes them builtin), and compiling from that. If I download the source for > 4.5, is there somewhere I can find a .config file that would allow for low- > latency performance? What do you mean by low-latency kernel? I'm not aware of any low-latency patches. There is the RT series, of course. But it's for bounded latency, not low latency. And as far as I know, it's not available for 4.5. If 4.5 doesn't pan out, you can try the patch below. It will disable LPM for all devices, and it should work with 4.2. See if it helps. Alan Stern --- usb-3.15.orig/drivers/usb/core/hub.c +++ usb-3.15/drivers/usb/core/hub.c @@ -130,6 +130,8 @@ struct usb_hub *usb_hub_to_struct_hub(st static int usb_device_supports_lpm(struct usb_device *udev) { + return 0; + /* USB 2.1 (and greater) devices indicate LPM support through * their USB 2.0 Extended Capabilities BOS descriptor. */ -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
