[PATCH 0/2] pinctrl: Enable support for external GPIO interrupts

[Linus Walleij]

On Wed, Jun 29, 2016 at 4:41 PM, Daniel Drake <drake at endlessm.com> wrote:

> On this hardware we only have 8 GPIO IRQs available, for 100+ GPIOs.
> If you want to monitor for both rising and falling edge of a GPIO then
> you have to use 2 GPIO IRQs. 2 are used for the common case of SD card
> detect. You can quickly lose several more (2 for audio jack detection,
> power button, etc). So these are a very limited resource.
>
> If the allocation is done dynamically I see 2 slight advantages:
>
>  1. If the number of GPIO-IRQ users is greater than the number
> available, the distributor can exclude drivers that are not of
> interest to him and the corresponding GPIO-IRQs will automatically and
> dynamically become available for the drivers that are of interest.
>
>  2. If the device tree encodes these assignments then the management
> could be a bit complex, because some will be defined in the SoC dtsi
> files and others will be defined in the board dts files (e.g.
> Endless's CVBS mode selection switch), we'll have to make sure that
> there are not conflicting assignments. Similarly if we end up sharing
> dtsi files over different SoC versions then things could get tricky
> especially in such a small namespace of 8 GPIO-IRQs. In the dynamic
> case this is not an issue.

I think I'm siding with Daniel's analysis.

These IRQs should be dynamically assigned, if practically feasible.

BTW isn't the hierarchical irqdomain invented for exactly this
usecase?

Yours,
Linus Walleij