From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marc Zyngier <marc.zyngier@arm.com>
Subject: Re: [RESEND PATCH v2 1/4] irqchip: gic: Change irq type check when
 extension is present
Date: Wed, 27 Aug 2014 11:36:35 +0100
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List-Id: devicetree@vger.kernel.org

Hi Jan,

On 27/08/14 10:55, Jan L=FCbbe wrote:
> Marc,
>=20
> On Fri, 2014-08-22 at 12:09 +0100, Marc Zyngier wrote:
>> Here, you're using it to program something that sits between the
>> device and the GIC. This is a separate block, with its own hardware
>> configuration, that modifies the interrupt signal. This should be
>> reflected in the device-tree and the code paths.
>>
>> You can probably model this as a separate irqchip for the few
>> interrupts that require this, or have it configured at boot time
>> (assuming the configuration never changes).
>=20
> It seems to me that using a separate irqchip for a simple inverter wo=
uld
> add the run-time overhead of passing through wrapper functions on eve=
ry
> IRQ. Do you have an idea how this could be avoided without using the
> gic_arch_extn feature?

Well, from the rather vague description, it could be slightly more than
a simple inverter, like being able to generate interrupts on both risin=
g
and falling edges. Sorry, but this is not the GIC as ARM has architecte=
d it.

Yes, the additional irqchip adds some overhead. But the DT has to
reflect the fact that there is something on the interrupt path that doe=
s
some form of conversion.

> As in the DT the actual IRQ polarity should be used, simply configuri=
ng
> the HW IRQ polarity in the bootloader is not enough without telling t=
he
> GIC driver which polarity is supported on which IRQ, right?

Looking a bit closer at things, what you describe in DT is the IRQ
polarity the interrupt controller sees. Nothing else should interpret
that field.

So it is legal (IMO) to have a device with an interrupt specifier
describing a rising edge interrupt, and yet have the device generating =
a
falling edge, with Mediatek's special sauce doing the conversion in bet=
ween.

Something will have to configure the polarity widget though, but that
can be left outside of the GIC.

Thanks,

	M.
--=20
Jazz is not dead. It just smells funny...