RFC: simplified RISC-V interrupt and clocksource handling

[hch@lst.de (Christoph Hellwig)]

On Thu, Jul 26, 2018 at 04:38:43PM -0700, Atish Patra wrote:
> 1. As per my understanding, timer interrupt now can't be registered as a 
> Linux IRQ now. Thus, /proc/interrupts will not be automatically populated 
> for timer interrupt stats. Am I wrong in my assumption?

Yes, with this code the timer interrupt does not show up in
/proc/interrupts.  I wonder if that is an issue and if there is any
precedence for it?

> 2. The future version of local interrupt controller known as Core Level 
> Interrupt Controller aka CLIC. Do we have to change the current design
> again for CLIC in future?
>
> Here are the docs:
> https://github.com/sifive/clic-spec/blob/master/clic.adoc

This doesn't really look like 'the future' version but a proposal for
something more like low end realtime microcontrollers ala ARM Cortex M*.
At least the priorities don't really make much sense for a general
purpose SOC.

Either way the existing architectural scause/sie interrupt handling will
remain but can be opted out, but if we really want to support the CLIC
it would have to grow a new irqchip driver, and the PLIC driver would
require a few dozend new lines of glue code to chain underneath it.