linux-kernel - Re: [PATCH 2/2] gpio: Support cascaded GPIO chip lookup for OF

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Message-ID: <CACRpkdb-movUA67=8WrCcYTO5WyAjUcur44R=vQ0iaBp-tMSmg@mail.gmail.com>
Date:	Mon, 13 Jun 2016 08:48:45 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Pantelis Antoniou <pantelis.antoniou@...sulko.com>
Cc:	Rob Herring <robherring2@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	Frank Rowand <frowand.list@...il.com>,
	Matt Porter <mporter@...sulko.com>,
	Koen Kooi <koen@...inion.thruhere.net>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Guenter Roeck <linux@...ck-us.net>,
	Marek Vasut <marex@...x.de>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 2/2] gpio: Support cascaded GPIO chip lookup for OF

On Wed, Jun 8, 2016 at 3:41 PM, Pantelis Antoniou
<pantelis.antoniou@...sulko.com> wrote:

> Devices that use interrupts usually convert the GPIO to an interrupt and use it.
> Since the xlat op will return the real GPIO spec the interrupt conversion will work.
>
> Bare interrupt lines are sort-of out of fashion nowadays I think. I’m eager to be
> proven wrong though with a recent portable expansion board that uses them.

No. We have established since several years back that gpiochip and interrupt
chip use cases are orthogonal, and there is absolutely *NO* requirement that
a consumer call .to_irq() on a GPIO line before using it as an interrupt, if the
driver exposes an interrupt chip.

It is true that external interrupt lines are out-of-fashion and usually replaced
with GPIOs that can trigger IRQs. However the latter have two interfaces
independent of each other.

A practical usecase is the SMSC911x ethernet drivers that have their IRQ
wired to both external interrupt lines and GPIO lines used as IRQ in different
use cases. It should not need to know whether the interrupt provider is a
"real" IRQ line or a GPIO line providing an IRQ. It just wants "some IRQ",
and this should be hidden from the driver and the hardware's DT bindings.

Yours,
Linus Walleij