linux-kernel - Re: [PATCH v3] Input: gpio_keys: Add level trigger support for GPIO keys

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Message-ID: <20180302004404.GA242226@dtor-ws>
Date:   Thu, 1 Mar 2018 16:44:04 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Baolin Wang <baolin.wang@...aro.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        gregkh <gregkh@...uxfoundation.org>,
        stephen lu <lumotuwe@...il.com>,
        Arvind Yadav <arvind.yadav.cs@...il.com>,
        Joseph Lo <josephl@...dia.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v3] Input: gpio_keys: Add level trigger support for GPIO
 keys

On Thu, Mar 01, 2018 at 03:35:23PM +0800, Baolin Wang wrote:
> On 28 February 2018 at 22:44, Arnd Bergmann <arnd@...db.de> wrote:
> > On Wed, Feb 28, 2018 at 1:44 PM, Baolin Wang <baolin.wang@...aro.org> wrote:
> >> On some platforms (such as Spreadtrum platform), the GPIO keys can only
> >> be triggered by level type. So this patch introduces one property to
> >> indicate if the GPIO trigger type is level trigger or edge trigger.
> >>
> >> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
> >> ---
> >> Changes since v2:
> >>  - Use 'interrupt' property to indicate the irq type.
> >>
> >> Changes since v1:
> >>  - Diable the GPIO irq until reversing the GPIO level type.
> >
> > I've looked at your patch in more detail now, and given it a bit more thought.
> >
> > I wonder if you could move that logic into your gpiochip/irqchip driver instead.
> > It seems that what you do in the gpio-keys driver is to emulate edge triggered
> > behavior on a level triggered irqchip.
> >
> > If you put the same logic into the gpio driver, you could simply make it
> > pretend to support an edge trigger on both edges and call into the interrupt
> > handler whenever the state changes.
> >
> 
> That is really a good suggestion, which can avoid duplicate level
> reverse logic in different drivers. So this patch can be simplified
> just adding one trigger_type to indicate the interrupt type (not
> always edge trigger). Thanks for your suggestion.

No, there is no need to add trigger type. The gpio-keys driver expects
trigger with both edges, falling and rising. If your GPIO chip does not
support it natively, you need to emulate edge trigger via level
interrupts by reprogramming trigger from active low to active high and
back on the fly. This should be done in the gpiochip/irqchip driver.
There is no need to change gpio-keys driver.

Thanks.

-- 
Dmitry