we are using the 88W8997 chip and gsm modem PHS8P(both on USB) in our device. We noticed, when we use gsm modem(send some AT command), wifi chip will stop working. With lots of debuging(looking into EHCI) we found out, when at least one URB on INT EP5 IN of modem's ttyUSB line is submited, all(6) 88W8997's OUT BULK URBs are stopped in processing. They are still in some structures in ehci, URB "complete function" is not called...
We tested kernel 4.1.52 on IMX53, 4.14, 4,19, 5.4 on IMX6, 5.7.9 on PC always with same result. For wifi we use driver from kernel(mwifiex) with Marvel's driver(mlan and mlinux) it was same. Modem is using driver option(usb_wwan).
Has anyone seen similar conflict on USB?