Re: [PATCH v2 6/7] pinctrl: mcp23s08: remove hardcoded irq polarity in irq_setup

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Fri, Oct 6, 2017 at 7:08 AM, Phil Reid <preid@xxxxxxxxxxxxxxxxx> wrote:

> The polarity of the irq could be altered
> by additional logic (eg inverters) between the device and irq input device.

Marc Zyngier has pointed out that inverters should be modeled
using hierarchichal irq domains. You would need to add a new
irqchip to invert the line.

See this PDF:
https://elinux.org/images/8/8c/Zyngier.pdf

drivers/irqchips/irq-uniphier-aidet.c supports inversion of IRQs
for example. For this it uses irq_domain_create_hierarchy()

I guess it would be helpful with a reusable generic "inverter
irq chip", that you can just enable and slam into your device
tree to tell the system that a line is statically inverted, i.e.
non-programmable logic on the board.

Yours,
Linus Walleij
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