MT7621 Soc Crypto Engine - IRQ not mapped - linux-device-driver

Question

I am using the latest Openwrt trunk firmware (kernel 4.3) and have successfully compiled the driver for its CryptoEngine, an internal ipsec accelerator of MT7621 Soc (which as far as I understood is on an internal bus called AMBA / APB).
The driver seems to work (CryptoEngine gets configured successfully by sending and receiving packets, so it does "react" on memory mapped registers).
However the driver is unable to hook up the irq (so it works only in polling mode), because request_irq always fails with error code 89 (EDESTADDRREQ Destination address required) on IRQ 19 (driver log does not give any error before) and I can't understand why (I am not a linux device driver expert, just a basic understanding, let's say that I managed to recompile the driver).
Any idea why this happens ? Could it be a problem with the board dts file ? Here follows the dmesg log and a link to the dts files used (Dmesg Log too long to include, Soc dtsi (dev.openwrt.org/browser/trunk/target/linux/ramips/dts/mt7621.dtsi) and Board dts))
CryptoEngine memory map 0x1E004000-0x1E004FFF
root#OpenWrt:/# lspci
00:00.0 PCI bridge: Device 0e8d:0801 (rev 01)
00:01.0 PCI bridge: Device 0e8d:0801 (rev 01)
00:02.0 PCI bridge: Device 0e8d:0801 (rev 01)
01:00.0 Network controller: MEDIATEK Corp. MT7662E 802.11ac PCI Express Wireless Network Adapter
02:00.0 Network controller: MEDIATEK Corp. MT7662E 802.11ac PCI Express Wireless Network Adapter
03:00.0 SATA controller: ASMedia Technology Inc. ASM1062 Serial ATA Controller (rev 01)
root#OpenWrt:/# cat /proc/interrupts
CPU0 CPU1 CPU2 CPU3
8: 63126 63253 63143 63987 MIPS GIC Local 1 timer
10: 1513 0 0 0 MIPS GIC 10 1e100000.ethernet
11: 2 0 0 0 MIPS GIC 11 mt76pci
29: 0 0 0 0 MIPS GIC 29 xhci-hcd:usb1
31: 2 0 0 0 MIPS GIC 31 mt76pci
33: 7976 0 0 0 MIPS GIC 33 serial
63: 1178 0 0 0 MIPS GIC 63 IPI call
64: 0 1305 0 0 MIPS GIC 64 IPI call
65: 0 0 1257 0 MIPS GIC 65 IPI call
66: 0 0 0 1087 MIPS GIC 66 IPI call
67: 144709 0 0 0 MIPS GIC 67 IPI resched
68: 0 25822 0 0 MIPS GIC 68 IPI resched
69: 0 0 97134 0 MIPS GIC 69 IPI resched
70: 0 0 0 43037 MIPS GIC 70 IPI resched
root#OpenWrt:/# cat /proc/ioports
ffffffff-ffffffff : /pcie#1e140000