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

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Message-ID: <bbc81e4d-7a3c-ef1e-e89b-739bc262f6db@siemens.com>
Date:   Fri, 26 Apr 2019 19:37:35 +0200
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     "Enrico Weigelt, metux IT consult" <lkml@...ux.net>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        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 19:20, Andy Shevchenko wrote:
> On Fri, Apr 26, 2019 at 7:05 PM Jan Kiszka <jan.kiszka@...mens.com> wrote:
>>
>> On 26.04.19 16:42, Enrico Weigelt, metux IT consult wrote:
>>> On 26.04.19 15:36, Jan Kiszka wrote:
>>>
>>>> At the same time, there are no real alternatives - to my> knowledge - for the value it brings (various bindings) to simply
>>> switch> the engine.
>>> Which value exactly does that collection of crude wrappers and broken
>>> attempts to buypass the kernel (driving gpios via /dev/mem *facepalm*)
>>> provide ?
>>
>> Leaving that blunt hack aside:
>>
>> import mraa
>>
>> pin = mraa.Gpio(13)
>> pin.dir(mraa.DIR_OUT)
>> pin.write(1)
>>
>> And the same goes for nodejs, java and c++.
>>
>> Moreover, this allows you to abstract away where "Pin 13" actually came from on
>> that board if the kernel changes (BSP -> upstream...) or the extension board or
>> ...
> 
> The problem here is opaque number. This has to be chip + *relative* pin number/
> See this:
> https://stackoverflow.com/questions/55532410/how-do-linux-gpio-numbers-get-their-values/55579640#55579640
> 

...and device path based discovery of the base:

https://github.com/siemens/mraa/commits/jan/queue

And I think that makes good use cases for application-level abstractions like in 
mraa. You don't want all user having to learn those nasty details, for 
devicetree, ACPI, and even worse stuff.

Jan

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