linux-kernel - Re: [PATCH 10/13] gpio: max77650: add GPIO support

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Date:   Tue, 29 Jan 2019 12:00:32 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Brian Masney <masneyb@...tation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>, Lee Jones <lee.jones@...aro.org>,
        Sebastian Reichel <sre@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Input <linux-input@...r.kernel.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH 10/13] gpio: max77650: add GPIO support

czw., 24 sty 2019 o 11:30 Linus Walleij <linus.walleij@...aro.org> napisał(a):
>
> On Mon, Jan 21, 2019 at 6:07 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
>
> > Thank you for your review. While I think you're right about the issue
> > being present in this driver, I'm not sure it's really a problem. Do
> > we actually require every gpio-controller to also be a stand-alone
> > interrupt-controller?
>
> Absolutely not :D
>
> Just GPIO is fine.
>
> > The binding document for the GPIO module doesn't
> > mention this - it only requires the gpio-controller property. Without
> > the "interrupt-controller" property dtc will bail-out if anyone uses
> > this node as the interrupt parent.
> >
> > If I'm wrong and we do require it, then I think we need to update
> > Documentation/devicetree/bindings/gpio/gpio.txt.
>
> What is weird is if a driver with DT bindings not mentioning IRQ
> and only probing from DT start implementing IRQ support, that
> becomes quite inconsistent. So then max77650_gpio_to_irq()
> should just return -ENOTSUPP
> or something for now, then it's fine.
>

I don't see it as weird at all. I see the need to define the register
and interrupt resources in DT for SoC peripherals becaue SoCs often
reuse IPs. But in the case of a self-contained i2c PMIC - the modules
such as GPIO are tightly coupled with the core functionality. In the
case of this device for example: there isn't even a separate set of
mask/status registers for GPIO interrupts.

Most mfd devices setup the resources in a hard-coded manner.

> We can add the (complicated) IRQ handling later.
>
> I am trying to eat my own dogfood here, I was sweating all
> last night trying to implement a hierarchical IRQ controller.
> There is no running away from that now. :/
>
> Apparently doing hierarchical IRQs demand that all irq
> controllers up to the top-level SoC IRQ controller support
> hierarchical interrupts using the v2 version of the irqdomain
> API, and currently it seems like the ARM
> GIC seems like the only top level IRQ controller that can
> do that.
>

Yep, and for that reason I can't use the regmap irq_chip abstraction
for now because it doesn't implement support for hierarchical
interrupts either.

How about the cascaded gpiochip irq_chip?

Best regards,
Bartosz