Re: [PATCH 0/7] serial: uartps: Revert dynamic port allocation

[Michal Simek]

On 03. 04. 20 17:48, Maarten Brock wrote:
> On 2020-04-03 11:51, Michal Simek wrote:
>>
>> Thanks. I am definitely interested to hear more how this could be done
>> differently because that hardcoded limits are painful.
>> On FPGAs you can have a lot of uarts for whatever reason and users are
>> using DT aliases to have consistent naming.
>> Specifically on Xilinx devices we are using uartps which is ttyPS,
>> uartlite which is ttyUL, ns16500 which is ttyS and also pl011 which is
>> ttyAMA.
>> Only ttyAMA or ttyPS on one chip are possible.
>>
>> And right now you can't have serial0 alias pointed ttyPS0 and another
>> serial0 pointed to ttyUL0 or ttyS0. That's why others are shifted and we
>> can reach that hardcoded NR_UART limit easily.
>> And this was the reason why I have done these patches in past to remove
>> any limit from these drivers and if user asks for serial100 alias you
>> simply get ttyPS100 node.
> 
> I would argue that the trouble originates from every uart driver using
> its own naming scheme and thereby creating separate namespaces. If all
> uarts would register as /dev/ttySnn then the serialN alias method would
> work. These non-overlapping namespaces is something the linux kernel
> driver community has allowed to happen.
> 
> If the namespaces are not abandoned and disallowed, then the serialN
> alias method must no longer be used for any driver that does not create
> /dev/ttySnn devices. Every namespace will require its own alias base.
> Or forget about deriving the number from an alias and set the number in
> a property in the device tree node itself. The latter has my preference.

Uartlite and as I see ucc_uart are only two driver which are using
port-number property for this purpose.
And IIRC this property was the part of any spec long time ago.

Thanks,
Michal