linux-kernel - Re: [PATCH 4/9] pinctrl: meson: allow gpio to request irq

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Date:   Wed, 26 Oct 2016 16:32:29 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Jerome Brunet <jbrunet@...libre.com>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        Carlo Caione <carlo@...one.org>,
        Kevin Hilman <khilman@...libre.com>,
        "open list:ARM/Amlogic Meson..." <linux-amlogic@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Rob Herring <robh+dt@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH 4/9] pinctrl: meson: allow gpio to request irq

On Wed, Oct 26, 2016 at 4:22 PM, Jerome Brunet <jbrunet@...libre.com> wrote:
> On Tue, 2016-10-25 at 20:20 +0200, Linus Walleij wrote:

>> However the semantic is such, that it is not necessary to call
>> to_irq()
>> before using an IRQ: the irqchip and gpiochip abstractions should be
>> orthogonal.
>
> Linus,
>
> They are orthogonal. You can request an irq from the irqchip controller
> without the gpiochip, like any other irq controller.

OK good, sorry if I'm stating the obvious.

> irq_create_mapping (and irq_create_fwspec_mapping) internally calls
> irq_find_mapping. So if the mapping already exist (the irq is already
> used before calling to_irq), the existing mapping will be returned. The
> mapping will be actually created only if needed. It seems to be in line
> with your explanation, no ?

Yes, but you want to call irq_create_mapping() in slowpath (irq setup)
and irq_find_mapping() in fastpath (irq handler). Else the first IRQ
may result in unwelcomed surprises.

> There is really a *lot* of gpio drivers which use irq_create_mapping in
> the to_irq callback, are these all wrong ?

Yes they are all wrong. They should all be using irq_find_mapping().

> If this should not be used, what should we all do instead ?

Call irq_create_mapping() in some other place.

Yours,
Linus Walleij