[U-Boot] [RFC] interrupt handling

[Albert ARIBAUD <albert.u.boot@aribaud.net>]

Hello all,

From time to time there is discussion about the need for proper
interrupt support in U-Boot.

Right now, the only thing left in the source code which remotely looks
like interrupt support is a few code sections compiled conditionally
under CONFIG_USE_IRQ, and it does not constitute a good approach to
interrupt support, if only for the following reasons:

- CONFIG_USE_IRQ is very general and imprecise as far as overall
  meaning goes. It does not say "allow drivers to use IRQs", or "IRQs
  are provided by supporting this specific interrupt controller", or
  "this driver requires IRQs to work". It does not help us either that
  the option was never documented...

- CONFIG_USE_IRQ is, OTOH, very specific as far as interrupt types go.
  IRQ is an acronym known in ARM for a specific type of interrupt, but
  ARM also knows FIQ. IRQ may have a different meaning for another
  architecture, and each platform has its own classification and
  attributes for interrupts.

- no API is defined for registering interrupt controller or interrupt
  client drivers.

But the worst part is, CONFIG_USE_IRQ is never *ever* defined. :)

So I am tempted to start this RFC with a first question: do we *need*
interrupts in the first place, and if we do, do we need an organized
interrupts subsystem or do we keep an ad hoc approach?

Amicalement,
-- 
Albert.