How would one extend an existing interrupt request to other processors? There is already an existing request that was made and enabled on a specific processor. I would like to extend this IRQ, which fires based off a hardware counter, such that there exists an IRQ for each of the processors, and if any of the IRQs are triggered, they are funnelled to the already existing IRQ and its handler. Essentially, I am trying to create an IRQ mux. Has anyone had any experience with this?
A better explanation is that the IRQ is the same across all processors. So, I would like to change an already requested and enabled IRQ (requested, enabled, and handled in a separate .c file) to a percpu IRQ within the new .c file
This doesn't sound like something you can expect to do in software.
Even if you could, the answer would depend a very great deal on exactly what CPU you are using, that CPU's support for multi-processing, any chipset or other supporting circuitry on your board, and so on.
I would expect the general answer to be "you can't do that", though. There are probably exceptions.