spi: bcm2835: driver for "auxiliar" spi1/spi2

[Jakub Kiciński]

On Thu, 18 Jun 2015 11:58:48 +0100, Mark Brown wrote:
> On Thu, Jun 18, 2015 at 12:19:04PM +0200, Noralf Trønnes wrote:
> 
> > There is also an aux mini uart that shares interrupt with spi1/2.
> > The AUXIRQ register determines the interrupt source. How should this
> > sharing be done? This uart is really only useful on the Compute Module
> > since it's pins overlap the pl011 uart pins on the other boards.
> > This is how the mini uart is used/setup downstream:
> > https://github.com/raspberrypi/linux/pull/1008
> 
> Linux supports shared interrupts perfectly fine, though it sounds like
> this is actually a cascaded interrupt (the demux is another interrupt
> controller) which we also support just fine.

Mark, could you give us a hint how to best go about this shared IRQ?
I failed to find any generic interrupt controller.  I imagine there
should be some fake irqchip we can instantiate from DT giving it a
irq line and a memory address and it should provide us with 32(bit)
demuxed irqs based on status of bits in specified memory location.
Does this sound reasonable?  Does such fake irqchip driver exist?