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

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Date:   Fri, 26 Apr 2019 19:52:48 +0200
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        "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 19:46, Manivannan Sadhasivam wrote:
> On Fri, Apr 26, 2019 at 07:39:56PM +0200, Jan Kiszka wrote:
>> 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?
>>
> 
> Good point! For tackling this, I'm planning to introduce an API for accessing
> the GPIO by its line name. It will be tricky to implement but once done, it
> will serve.

Whatever is stable and handy. As cited in the other thread, I played with the 
device path as well, see [1][2]. Feel free to pick what what is useful, I will 
likely not have time to work on that soon again.

Jan

[1] https://github.com/siemens/mraa/commit/034d787eea1a5b201ea77a6549ffc0bdbc3b776d
[2] https://github.com/siemens/mraa/commit/6fd8a3c27764718c1e62a4938a6dc88819c3f65f

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