On Sat, Jan 22, 2022 at 01:49:44PM +0100, Sander Vanheule wrote:
> Hi Rob,
>
> On Fri, 2022-01-21 at 16:56 -0600, Rob Herring wrote:
> > On Sun, Jan 09, 2022 at 03:54:35PM +0100, Sander Vanheule wrote:
> > > The interrupt router has 32 inputs and up to 15 outputs, and the way
> > > these are mapped to each other is runtime configurable. The outputs of
> > > this interrupt router on the other hand, are connected to a fixed set of
> > > parent interrupts. This means that "interrupt-map" is inappropriate, and
> > > rather a list of parent interrupts should be specified.
> >
> > I'm not sure why interrupt-map is not appropriate. It is not appropriate
> > if you have to touch the interrupt router h/w in servicing the
> > interrupts. If you just need one time configuration of the mapping, then
> > it should be fine to use I think.
>
> If interrupt-map is used, then AFAICT there are no hooks to inform the driver that a
> translation has occurred. How should the interrupt controller driver then know how to set
> up the routing? Commit de4adddcbcc2 ("of/irq: Add a quirk for controllers with their own
> definition of interrupt-map") added a quirk for the original binding/driver, but that
> requires open-coding an interrupt-map parser in the driver.
The issue was not open-coding parsing, but was the need for something in
the middle to service the interrupt. As 'interrupt-map' should be a
transparent remapping or routing.
>
> What this binding doesn't mention (I can add it), is that there are also two IRQ status
> registers to:
> - unmask/mask SoC interrupts
> - read the current status of the SoC interrupts
That would not be transparent.
> In theory, if the routing is set up correctly (and the IRQ permanently unmasked), I think
> one could treat interrupt-map as intended, and connect SoC peripheral IRQ handlers
> directly to the parent interrupts. But then the interrupt subsystem would need to check
> all attached handlers. This interrupt router/controller allows to check which peripheral
> is triggering the parent IRQ, which should be more efficient.
>
> These interrupt controllers are also used on multi-threaded systems, where each hardware
> thread has its own IRQ controller. I'm still experimenting with the implementation, but
> there the routing registers would be used to set the CPU affinity of SoC interrupts.
>
> I have to say that I'm not very familiar with the kernel code that handles all this
> though, so maybe I'm just missing something?
Okay, seems 'interrupt-map' is indeed not appropriate here.
Rob
