Hi,
On Tue, Nov 21, 2017 at 05:04:51PM +0100, Alexander Stein wrote:
> Hi,
>
> On Tuesday, November 21, 2017, 4:21:42 PM CET Sebastian Reichel wrote:
> >[...]
> > --------------------------------------------
> > gpio: host-gpio {
> > random-properties;
> > }
> >
> > inv: line-inverter {
> > /*
> > * configure the gpio controller input to be active low
> > * and the inverter interrupt output to be active low
> > */
> > interrupts = <&gpio ACTIVE_LOW>;
> > };
> >
> > mcp23xxx {
> > random-properties;
> >
> > /*
> > * configure the chip interrupt output to be active high
> > * and the inverter interrupt input to be active high
> > */
> > interrupts = <&inv ACTIVE_HIGH>;
> > }
> > --------------------------------------------
> >
> > versus
> >
> > --------------------------------------------
> > gpio: host-gpio {
> > random-properties;
> > }
> >
> > mcp23xxx {
> > random-properties;
> >
> > /* configure host interrupt input pin to be active low */
> > interrupts = <&gpio ACTIVE_LOW>;
> >
> > /* configure chip interrupt output pin to be active high */
> > microchip,irq-active-high;
> > }
> > --------------------------------------------
> >
> > I think this is something, that Rob should comment on. Obviously at
> > least in the mainline kernel nobody implemented the first solution
> > (since there is no fitting interrupt-invert driver), but there are
> > a few instances of the second variant. On the other hand the first
> > solution describes the hardware more detailed.
> >
> > > And if someone is relying on that implicit behaviour are we allowed
> > > to break things? Probably ok with this one as it's currently not possible
> > > due to code patch 1 removes.
> > >
> > > If we need to model the invert to get the patches accepted I look into that.
> > > I don't actually need it for my system as I can set open-drain with overrides
> > > the active-high control on this device, while have active high irq consumer.
> > > :)
> >
> > IMHO the explicit line-inverter is a bit over-engineered and
> > implicit line-inverter is enough, but I'm fine with both solutions.
> > I think the DT binding maintainers should comment on this though,
> > since it's pretty much a core decision about interrupt specifiers.
>
> Once you have a hardware, where one of several IRQ users is not attached to the
> inverter you need this inverter node anyway, caused by the mixed polarities.
> Also some IRQ controllers, like ARM GIC, only support rising edge interrupts
> (also level high).
>
> This might get important if there are dedicated IRQ pads connected to several
> users.
Both binding formats support this use-case as far as I can tell.
Since you seem to understand how it looks like with the inverter
node here is an example without it:
irqctrl: irq-controller {
random-properties;
}
mcp23xxx0 {
random-properties;
/*
* configure host interrupt input pin to be active high, since
* nothing else is supported by the interrupt controller
*/
interrupts = <&irqctrl ACTIVE_HIGH>;
/*
* configure chip interrupt output pin to be active low due to
* line invert
*/
microchip,irq-active-high;
}
mcp23xxx1 {
random-properties;
/*
* shared irq, see description from other chip
*/
interrupts = <&irqctrl ACTIVE_HIGH>;
/*
* configure chip interrupt output pin to be active high, since
* it's routed through the line invert
*/
/* microchip,irq-active-high; */
}
-- Sebastian
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