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Legacy imx31/51 USB OTG under linux arcotg.ko spurrious interrupt

Question asked by Andrew Robinson on Apr 13, 2014
Latest reply on Apr 14, 2014 by Andrew Robinson

During manual linux kernel driver initialization of the USB-otg gadget drivers typically used in SONY readers PRS900 and above, I am getting spurrious interrupts on irq 37.  It happens when the USB cable is not plugged in before the arcotg.ko driver loads for the first time for device/slave mode usb usage.


IT's reproduceable on a sonyPRS900 with the following code, reliably:  ( modules_09xx.tgz or modules_10xx.tgz)


The interrupt happens on IRQ 37 which is the interrupt normally associated with USB data transfer on the iMX31.

When the interrupt happens, none of the flags in the usb_dr_device (imx31 OTG hardware registers) indicate an interrupt has happened, and the host is stopped, etc.  eg: usbsts (USB Status Register) is clear.

Nor does pre-clearing the interrupts in the otgsc register solve the problem.


Although I have looked, I am having trouble finding hardware data sheets which describe interrupt sources for the USBOTG core in the iMX31, and how they are accessed/masked and routed to IRQ 37.  I believe, a PHY isp1504 may be present;


Where do I find information on how *ALL* the interrupts of the iMX31 are generated for USB-OTG, serviced, and masked at the hardware level so I can figure out how to mark the spurrious interrupt as serviced?

Failure to do so causes the interrupt to be disabled all together by the linux kernel after ~32 failed requests and the driver no longer works or detects cable plug ins or removals.