[PATCH] ARM: dts: stm32: Fill GPIO line names on AV96

[Marek Vasut]

On 3/12/21 4:17 PM, Christoph Niedermaier wrote:
> From: Marek Vasut [mailto:marex at denx.de]
> Sent: Thursday, August 6, 2020 9:30 AM
> 
>> On 8/6/20 9:09 AM, Christoph Niedermaier wrote:
>>> From: Marek Vasut <marex at denx.de>
>>> Sent: Friday, July 24, 2020 12:16 PM
>>>>
>>>> Fill in the custom GPIO line names used by DH.
>>>>
>>> [...]
>>>> +&gpioa {
>>>> +       gpio-line-names = "", "", "", "",
>>>> +                         "", "", "", "",
>>>> +                         "", "", "", "DH-GPIO-K",
>>>> +                         "DH-GPIO-I", "", "DH-GPIO-A", "";
>>>> +};
>>>> +
>>> [...]
>>>
>>> We have been using the GPIO names at DH electronics for some time and also
>>> on other SOMs, but have not yet streamed them. We started with the naming
>>> only with a capital letter "A-W" since then without problems. To avoid a
>>> hard cut or patching for us and our customers it would be good if we could
>>> use the same naming in the mainline kernel as well. Marek, we would be
>>> happy if you would adopt our valued GPIO naming in your patch.
>>
>> My counter-argument to this is that the naming should be unique and
>> provide a hint where those GPIO lines come from, so maybe even DH-GPIO-n
>> should rather be DHCOM-n . I can't say I'm particularly fond of the
>> plain 'n' naming of GPIO lines, because then the GPIO label (and e.g.
>> listing in libgpiod tools) does not give any hint what the GPIO is or
>> where it comes from. Also, I worry a plain 'n' naming might clash with
>> other GPIO IPs easily, while a more unique name can not.
> 
> Hello Marek,
> 
> after an internal discussion, we decided the following:
> 
> Could you update the patch for the Avenger96 to the GPIO naming "AV96-n".
> 
> Moreover for the SOM layer (stm32mp15xx-dhcom-som.dtsi) we would prefer
> "DHCOM-n". It would be nice if you could create a patch for it.

I don't think we should have any SoM-side gpio-line-names, because once 
you plug the SoM into new carrier board, the gpio-lane-names will no 
longer make sense. So, I think all the gpio-line-names should be 
implemented in the carrier board DTS.

As for the naming scheme, I was also hoping Linus might jump in and 
provide some suggestion on best practice here.

I think naming carrier board GPIOs "A", "B", "C",... is too opaque and 
can easily collide e.g. with GPIO expanders which might be on I2C or so.

A naming scheme which encodes the carrier board name is clearer and less 
likely to cause collision, so "AV96-A", "AV96-B", etc. looks good to me. 
It is obvious where the GPIO is located and unlikely to collide with any 
other GPIO name.