Re: [PATCH v12 3/4] soc: microchip: add mpfs gpio interrupt mux driver

[Conor Dooley <conor@kernel.org>]

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On Mon, Mar 16, 2026 at 10:27:15AM +0100, Linus Walleij wrote:
> On Wed, Mar 11, 2026 at 4:18 PM Conor Dooley <conor@kernel.org> wrote:
> 
> > From: Conor Dooley <conor.dooley@microchip.com>
> >
> > On PolarFire SoC there are more GPIO interrupts than there are interrupt
> > lines available on the PLIC, and a runtime configurable mux is used to
> > decide which interrupts are assigned direct connections to the PLIC &
> > which are relegated to sharing a line.
> >
> > Add a driver so that Linux can set the mux based on the interrupt
> > mapping in the devicetree.
> >
> > Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
> 
> Reviewed-by: Linus Walleij <linusw@kernel.org>
> 
> We need a piece of accessible documentation that clearly defines
> the difference between an IRQ mux and a hierarchical IRQ chip.
> If only a post on people.kernel.org, just something to help people
> to know when to use which approach.

I'm guessing you're not looking for looking for me to be the arbiter,
but I'd say that the muxing aspect is pretty important!
On a serious note though, the lack of anything in the hardware to do
masking etc is key, it'd have to be nothing more than a register that
determines routing.
That said, even the simplest mux should be an irqchip if reconfiguration
after probe is to be supported.
That'd make the delimiter "a simple mux that you set at probe and never
touch again"?

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