Issues with request_irq on 4.9.30-bone4

I have an issue installing an interrupt handler in a hardware driver, in this specific case for the am3358 e-capture unit eCAP0 on a Beaglebone Green.

I am running a build per, built with a Mainline 4.9.30-bone4 (non real time) kernel and the debian-8.7-minimal-armhf-2017-01-14 file system.

The driver was developed and worked on an earlier 3.8 kernel, but now fails to receive any interrupts under the 4.9 kernel.

The interrupt is registered with a call to:

status = request_irq(31, ecap_interrupt, 0, ECAP_NAME, &ecap_data.devid);

31 is the interrupt number for eCAP0INT per table 6.3 in am335x-techref.

The call succeeds with a zero status, but the interrupt routine is never called even though events are detected by the eCAP unit.
Furthermore, looking at the /proc/interrupts I see:

22: 103 INTC 14 Level 49000000.edma_ccerrint
26: 0 INTC 96 Level 44e07000.gpio
31: 0 44e07000.gpio 4 Edge ecap
33: 0 44e07000.gpio 6 Edge 48060000.mmc cd
59: 0 INTC 98 Level 4804c000.gpio
92: 0 INTC 32 Level 481ac000.gpio

Which shows that (1) no interrupts have been detected on IRQ 31, and (2) the third column lists a suspicious “44e07000.gpio” instead of INTC as most other interrupt lines do. The latter leads me to believe that the interrupt is not mapped appropriately from the capture unit, but rather to some sort of gpio mapping, although I do not know what the third and the fourth column in /proc/interrupts show.

An attempt to probe for the interrupt using this code also fails with no detected interrupts:

do {
iowrite16(0x0000, &ecap_data.pecap[ECAP_ECEINT]); // Disable all interrupts
iowrite16(0x00ff, &ecap_data.pecap[ECAP_ECCLR]); // And clear status
mask = probe_irq_on();
iowrite16(0x0010, &ecap_data.pecap[ECAP_ECEINT]); // Re-enable CEVT4 interrupt
iowrite16(0x0010, &ecap_data.pecap[ECAP_ECFRC]); // And force-trigger it
istatus = probe_irq_off(mask);
if (istatus == 0) {
printk(KERN_INFO "No interrupt reported\n");
} while (istatus <= 0 && count++ < 5);

It sure looks to me that there is some sort of interrupt mapping/enabling that is new with the 4.x kernels which I am missing.

Any help and explanation would be greatly appreciated!