How to represent active low ARM GIC interrupts, enabled by external inverter?

[Russell King - ARM Linux]

On Mon, Jan 23, 2012 at 01:18:50PM -0800, Stephen Warren wrote:
> I'd like guidance on how to model one aspect of Tegra's interrupt
> structure.
> 
> Tegra has an interrupt input pin for use by a PMU chip.
> 
> The PMC HW module within Tegra can optionally invert this signal, but
> otherwise has no control over it; no interrupt status bits, no masking,
> etc.
> 
> The (potentially inverted) signal is then fed into the ARM GIC, which
> supports level high or rising edge interrupts only.

When I originally added the IRQ trigger types to request_irq(), the
original intention was for these to be specified by the requesting
driver according to what the chip required, and there to be some kind
of hook to deal with the inversion which happens on some boards.

However, that was never implemented because there was a far better
solution: pass this information to the driver via the device resource
structures, which already have this information defined for PNP
devices.  The driver would then find the IRQ resource which would
tell it both the number and the IRQ trigger flags to be used.

Some drivers have done this, to cope with differing wiring on boards.
I don't know if DT supports this though, but I'd suggest that it's
a solution worth investigating.