linux-kernel - Re: [PATCH 2/2] gpio: sch: Add interrupt support

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Message-ID: <CACRpkdY=m1QJVqvERiAY+7taUgjPXn=9U2Eajx7d7NPo-iNhiA@mail.gmail.com>
Date:   Fri, 26 Apr 2019 16:41:16 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     Jan Kiszka <jan.kiszka@...mens.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH 2/2] gpio: sch: Add interrupt support

On Fri, Apr 26, 2019 at 3:06 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
> On Wed, Apr 24, 2019 at 12:39:35PM +0200, Jan Kiszka wrote:
> > On 24.04.19 12:33, Mika Westerberg wrote:
> > > On Wed, Apr 24, 2019 at 12:19:02PM +0200, Jan Kiszka wrote:
>
> > > > And even if that were possible, we would be back to the square of existing
> > > > devices without those definitions. If this were a recent chipset, I would
> > > > say, "go, fix future firmware versions". But this one is legacy.
> > >
> > > Is it fixing some real issue with these legacy platforms? I mean without
> > > the patch some GPE event is not handled properly? It was not clear to me
> > > from the commit message.
> > >
> >
> > Without that patch, you are forced to poll for event changes in your
> > application, timer-driven. There are application that cannot process these
> > GPIOs because they lack such logic (mraa with node-red-node-intel-gpio is a
> > public example).
>
> Just a side note: MRAA is a hack itself. It abuses almost all interfaces Linux
> kernel provides.

I think it's pretty clean for GPIOs these days. My colleague Manivannan
was part of cleaning it up a while back and since then it is doing
what userspace should be doing if userspace absolutely cannot
abstain from using GPIOs directly (i.e. uses the character device).
https://github.com/intel-iot-devkit/mraa/blob/master/src/gpio/gpio_chardev.c

I don't know about other resources than GPIOs though.

Yours,
Linus Walleij