>30% CPU load increase with USB FLash plugged in (lots of SOF interrupts)

Hi,

I have a Cyclone V (kernel 4.1.22-ltsi-rt) with an USB3320 transceiver connected to USB1. There is a USB2422 HUB (2 port) connected to USB3320. One of the ports is connected to a 4 port CY7C65630.

CV <--> USB3320 <--> USB2422  <-port 2-> CY7C65630 <-4-ports-> (unused)
                                                             |
                                                            <-port 1->  USB Flash
  

When I plug-in a USB flash to USB2422 (port 1), CPU load increases by ~30% (two IRQ 36 handlers). I've found out that this is mainly due to the Start-of-Frame (SOF) interrupts being triggered every 125us. I have also enabled CONFIG_USB_DWC2_TRACK_MISSED_SOFS in the kernel and I get a dump of first 1000 missed SOFS very quickly.

Except from the above, the USB Flash is mounted and can be used without a problem.

My question is, is the CPU load normal or have I configured something incorrectly?

usbphy0: usbphy@0 {

# phy-cells = <0>;

compatible = "usb-nop-xceiv";

status = "okay";

};

usb0: usb@ffb00000 {

compatible = "snps,dwc2";

reg = <0xffb00000 0xffff>;

interrupts = <0 125 4>;

clocks = <&usb_mp_clk>;

clock-names = "otg";

phys = <&usbphy0>;

phy-names = "usb2-phy";

status = "disabled";

};

usb1: usb@ffb40000 {

compatible = "snps,dwc2";

reg = <0xffb40000 0xffff>;

interrupts = <0 128 4>;

clocks = <&usb_mp_clk>;

clock-names = "otg";

phys = <&usbphy0>;

phy-names = "usb2-phy";

status = "disabled";

};

BR mrkozmic