It is required to write software irq (120) handler and register it.
But request_irq return -38 (ENOSYS). How can I do it?
The use_irq inside request_irq() have been changed across kernel version. You need to use the result of irq_create_mapping() or irq_of_parse_and_map().
It may be due to your IRQ number - it has to be virtual, not the hardware IRQ.
And to quote:
"arch/ppc or arch/powerpc?
If the latter, you need to translate the hardware IRQ into a virtual
IRQ. The easiest way to do this is to put the DMA node into the device
tree and use of_irq_to_resource(). "