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

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Message-ID: <63b179c9-242d-ae90-9c33-49ed256bde28@siemens.com>
Date:   Fri, 26 Apr 2019 17:44:10 +0200
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     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 26.04.19 16:41, Linus Walleij wrote:
> 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.

That's valuable progress!

OTOH, there still seem to be the broken pattern to address pins via hard-coded 
GPIO numbers. This broke our neck, e.g., when trying to replace the hacky BSP 
kernel with upstream. I started to create better infrastructure but never fished 
that.

Thanks,
Jan

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