Re: [PATCH v2 tty-next 1/2] dt-bindings: serial: ni,ni16650: add bindings

Krzysztof Kozlowski
2023-04-13T07:40:05Z

On 13/04/2023 00:24, Brenda Streiff wrote:
> On 4/11/23 00:44, Krzysztof Kozlowski wrote:
>> On 10/04/2023 23:11, Brenda Streiff wrote:
>>> +
>>> + interrupts:
>>> + maxItems: 1
>>> +
>>> + clock-frequency: true
>>
>> I missed it last time - why do you need this property? You do not have
>> any clock input, so which clock's frequency is it?
>>
>
> This is the clock frequency of the UART; on our x86-based platforms this
> comes from the LPC clock, on Zynq-7000 it's derived from a clock in the
> FPGA. This is used to set struct uart_port::uartclk in the serial core,
> as it is for other UARTs.
>
> This clock frequency can vary based on board design (especially on the
> x86 side, due to different LPC clocks) but for a given design is fixed-
> frequency.

So you must have clock input - clocks property. Once you add this, use
assigned-clocks to get the rate you want.

>
> Would you prefer this be documented further? I was following 8250.yaml's
> lead here with the simple `true`.

I prefer to drop it. It is not correct and a legacy property. Without
clock inputs how can you even configure some clock?

Best regards,
Krzysztof