Re: DT Query on "New Compatible vs New Property"

[Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>]

On 28/02/2024 15:02, Sudeep Holla wrote:
> On Wed, Feb 28, 2024 at 02:27:30PM +0100, Ulf Hansson wrote:
>> On Mon, 26 Feb 2024 at 15:24, Nikunj Kela <quic_nkela@quicinc.com> wrote:
>>>
>>> Hi Sudeep,
>>>
>>> I would like to conclude on this thread. I was discussing this with Ulf.
>>> He thinks that using the domain names to identify if platform is
>>> abstracting clocks etc. are not scalable and sufficient. Instead he
>>> thinks that the change in the interface to OS(and FW) is a good
>>> candidate for a new compatible(even though HW is same).  Even for SCMI,
>>> we do change phandle in DT to SCMI protocol phandle so that is like a
>>> different platform altogether. Could you please let me know if you still
>>> think that using a different compatible in this case is not warranted.
>>
>> My apologies for joining this discussion at this late state. Yet, I
>> just wanted to confirm what Nikunj said above.
>>
>> In the end we are indeed talking about adding a new platform, as
>> changing the FW interface from a QCOM proprietary one into SCMI,
>> simply requires updates to a DTS file(s) that is platform specific.
>>
> 
> The way I read this sounds like all this are platform specific and need
> new compatible.
> 
>> That said, it also seems reasonable to me to use a compatible string,
>> to allow us to describe the update of HW for various affected devices.
>>
> 
> While I agree with the above statement, it depends on what you refer as
> update of HW above. It is all Qcom specific and there is so much turn
> between SoCs that this shouldn't matter but I would like to take example
> and describe what I initially mentioned/argued against.
> 
> Lets us assume 2 SoCs: A and B. A is old and didn't use SCMI while B is
> new and migrated to use SCMI. Now let us assume both A and B SoCs have
> exact same version/revision of an IP: X. Now just because B uses SCMI,
> should X have one compatible to be used in A and another in B. That
> doesn't sound right IMO.

That's trivial to answer, because these are different SoCs. Compatibles
are SoC specific and every SoC-IP-block needs its compatible. Rob was
repeating this many times that versioned compatibles are discouraged.

> 
> If X on A has to manage clocks and voltage separately while the same X
> on B uses SCMI to manage them together as performance domain, then the
> presence(or absence) of those properties must indicate the difference and
> not a change in compaible for the IP X. But it is upto Qcom platform
> maintainer, IP driver maintainer and DT maintainers to decide, I will
> leave that them. I just wanted to express my opinion on the matter.




Best regards,
Krzysztof