Re: [PATCH V2 1/2] dt-bindings: serial: add Broadcom's BCMBCA family High Speed UART

["Rafał Miłecki" <zajec5@gmail.com>]

On 22.11.2023 16:37, Krzysztof Kozlowski wrote:
> On 22/11/2023 16:32, Rafał Miłecki wrote:
>> On 22.11.2023 16:00, Krzysztof Kozlowski wrote:
>>> On 22/11/2023 15:52, Rafał Miłecki wrote:
>>>>>> +maintainers:
>>>>>> +  - Rafał Miłecki <rafal@milecki.pl>
>>>>>> +
>>>>>> +allOf:
>>>>>> +  - $ref: serial.yaml#
>>>>>> +
>>>>>> +properties:
>>>>>> +  compatible:
>>>>>> +    items:
>>>>>> +      - enum:
>>>>>> +          - brcm,bcm4908-hs-uart
>>>>>> +          - brcm,bcm4912-hs-uart
>>>>>> +          - brcm,bcm6756-hs-uart
>>>>>> +          - brcm,bcm6813-hs-uart
>>>>>> +          - brcm,bcm6846-hs-uart
>>>>>> +          - brcm,bcm6855-hs-uart
>>>>>> +          - brcm,bcm6856-hs-uart
>>>>>> +          - brcm,bcm6858-hs-uart
>>>>>> +          - brcm,bcm6878-hs-uart
>>>>>> +          - brcm,bcm47622-hs-uart
>>>>>> +          - brcm,bcm63138-hs-uart
>>>>>> +          - brcm,bcm63146-hs-uart
>>>>>> +          - brcm,bcm63158-hs-uart
>>>>>> +          - brcm,bcm63178-hs-uart
>>>>>> +      - const: brcm,bcmbca-hs-uart
>>>>>
>>>>> git grep did not find driver for this compatible. Is it in separate
>>>>> patchset?
>>>>
>>>> No. My project based on BCMBCA has been canceled and I don't work on it
>>>> full time anymore. I just wanted to fill empty bits I can afford
>>>> handling in my free time and complete hardware description in DTS.
>>>>
>>>> I may still work on some BCMBCA drivers from time to time but as a side
>>>> project.
>>>
>>> This means we cannot use driver to verify whether the fallback is
>>> actually suitable. Considering that existing UART bindings do not
>>> fallback (brcm,bcm6345-uart, brcm,bcm7271-uart), I don't understand what
>>> is the benefit here.
>>
>> I believed the rule for maintaining bindings and DTS files was to
>> describe hardware no matter what/if system needs it.
>>
>> For example a year ago I added binding for BCMBCA SoC timer without
>> actual driver, see e112f2de151b ("dt-bindings: timer: Add Broadcom's
>> BCMBCA timers").
>>
>> I'm not sure if we're going to agree on this, but personally I like
>> describing hardware as much as I can. So it's well documented /
>> understood and people may eventually write drivers for it. Maybe it's
>> partially because I come from Broadcom's world that isn't well known
>> for upstream efforts in general.
> 
> The problem is that "brcm,bcmbca-hs-uart" is not describing hardware. It
> is saying that all these devices have similar (compatible) programming
> model, so the OS can use just one compatible. This goes away from pure
> hardware description into interpretation.
> 
> Rob already commented on such non-SoC compatibles multiple times. I do
> not see any reason here to not use specific compatible as fallback.

Do I get it right we should rather have some base specific compatible
like: "brcm,bcm63138-hs-uart" and then if anything use fallback to it
like: "brcm,bcm4908-hs-uart", "brcm,bcm63138-hs-uart"; ?