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

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Date:   Wed, 12 Apr 2023 17:24:02 -0500
From:   Brenda Streiff <brenda.streiff@...com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     ilpo.jarvinen@...ux.intel.com,
        Gratian Crisan <gratian.crisan@...com>,
        Jason Smith <jason.smith@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 tty-next 1/2] dt-bindings: serial: ni,ni16650: add
 bindings

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.

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