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

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Date:   Wed, 24 Apr 2019 13:46:13 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Jan Kiszka <jan.kiszka@...mens.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-gpio@...r.kernel.org, linux-acpi@...r.kernel.org,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH 2/2] gpio: sch: Add interrupt support

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:
> > > > I think what you want is "GPIO signaled ACPI event". It works so that
> > > > you declare _AEI method below the GPIO controller listing the GPIOs you
> > > > want to trigger events for and then either _Lxx, _Exx or _EVT method for
> > > > each of them under the same controller. GPIO core then handles it
> > > > automatically when you register the GPIO chip. See also
> > > > acpi_gpiochip_request_interrupts().
> > > 
> > > Right, that is was I read as well. Let's assume I would be able to patch the
> > > tables: Would I describe all the logic of this patch in ACPI terms? Where to
> > > enable interrupts, how to dispatch the SCI event, how to acknowledge it
> > > etc.? Will it also take care of locking? (BTW, my locking seems to have some
> > > remaining inconsistency, on second look.)
> > 
> > The GPIO core would then take care of it by requesting the GPIO in
> > question and dispatching to the correct event handler. In this patch you
> > just leave out the SCI part and only implement the irqchip like you did
> > already.
> 
> Could you point me to a gpio driver that works like that already? Would be
> easier to learn that from an example. That infrastructure with all its
> different modes is seriously complex and not very well documented.

Pretty much all drivers under drivers/pinctrl/intel.

> > > 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).

But those are using the GPIOs via sysfs or the char device which should
work without the SCI handling part of your patch, no?