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

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Date:   Fri, 26 Apr 2019 19:39:56 +0200
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        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 19:33, Manivannan Sadhasivam wrote:
> On Fri, Apr 26, 2019 at 08:20:19PM +0300, 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
>>
> 
> But for platform like 96Boards we don't need controller specific lookup, these
> are all handled by the platform code [1] so that the users can use the standard
> pinout number to access GPIOs. For instance, pin 23 on the Low Speed expansion
> header is the GPIO for all 96Boards platform, so the user can access that pin
> using 23 itself in the application and it will run across all supported
> 96Boards.

Can you ensure stable numbering when probing order changes, e.g. due to adding 
an extension board?

Jan

> 
> That's one of the reason why we prefer MRAA.
> 
> Thanks,
> Mani
> 
> [1] https://github.com/intel-iot-devkit/mraa/blob/master/src/arm/96boards.c#L75
> 
>> -- 
>> With Best Regards,
>> Andy Shevchenko

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