linux-kernel - Re: [PATCH] pinctrl: armada-37xx: Add edge both type gpio irq support

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Message-ID: <CACRpkdZxWwXcB8o4+gsYN+mnoQvE7eT5sPOO1mKNuELuo7T70g@mail.gmail.com>
Date:   Tue, 31 Oct 2017 14:27:13 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Gregory CLEMENT <gregory.clement@...e-electrons.com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jason Cooper <jason@...edaemon.net>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Antoine Tenart <antoine.tenart@...e-electrons.com>,
        Miquèl Raynal <miquel.raynal@...e-electrons.com>,
        Nadav Haklai <nadavh@...vell.com>,
        Victor Gu <xigu@...vell.com>, Marcin Wojtas <mw@...ihalf.com>,
        Wilson Ding <dingwei@...vell.com>,
        Hua Jing <jinghua@...vell.com>,
        Neta Zur Hershkovits <neta@...vell.com>,
        Ken Ma <make@...vell.com>
Subject: Re: [PATCH] pinctrl: armada-37xx: Add edge both type gpio irq support

On Tue, Oct 31, 2017 at 2:16 PM, Andrew Lunn <andrew@...n.ch> wrote:

>> The discussion here is interesting, it is customary for GPIO drivers
>> to implement double-edge detection emulation by swapping the
>> edge detector around like this.
>
> Hi Linus
>
> I was not aware this was customary.
>
>> It might be possible to collect some generic information about
>> this in the Documentation/gpio/driver.txt document.
>
> Yes, i think it should be documented somewhere. Even in the use case
> here, detecting an SD card being inserted/removed, you could get some
> bounce on the microswitch, miss an edge, and be in the wrong state.

Indeed :/

This is I guess why it is a good idea to combine this with the
debounce feature if the hardware supports it.

I'll think about some writeup.

Yours,
Linus Walleij