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

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

On 24/01/2024 09:39, Manivannan Sadhasivam wrote:
> On Wed, Jan 24, 2024 at 09:02:16AM +0100, Krzysztof Kozlowski wrote:
>> On 23/01/2024 17:12, Manivannan Sadhasivam wrote:
>>> On Thu, Dec 14, 2023 at 07:18:25AM -0800, Nikunj Kela wrote:
>>>>
>>>> On 12/13/2023 11:49 PM, Krzysztof Kozlowski wrote:
>>>>> On 14/12/2023 07:17, Manivannan Sadhasivam wrote:
>>>>>> On Tue, Dec 12, 2023 at 11:06:42AM -0800, Nikunj Kela wrote:
>>>>>>> + Linaro team
>>>>>>>
>>>>>>> On 12/12/2023 11:01 AM, Krzysztof Kozlowski wrote:
>>>>>>>> On 12/12/2023 18:45, Nikunj Kela wrote:
>>>>>>>>> We are abstracting some resources(ex. clocks) under new firmware on an
>>>>>>>>> existing platform therefore need to make changes in certain drivers to
>>>>>>>>> work with that firmware. We need to make a distinction between two
>>>>>>>>> different variants of the FW. In one case, some resources will be
>>>>>>>>> abstracted while in other case, they won't be abstracted. My query is -
>>>>>>>>> "should we define a new compatible string for the variant with
>>>>>>>>> abstracted resources(in FW) or we should add a new DT property keeping
>>>>>>>>> the compatible same?"
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> Usually change in the interface or behavior warrants new compatible.
>>>>>>>> Property would be suitable if the same device, e.g. same SoC component
>>>>>>>> with same FW, was configured differently on different boards.
>>>>>>>>
>>>>>> Here, the hardware is going to be the same, but the resources (clocks,
>>>>>> regulators, etc...) will be controlled by the firmware instead of OS.
>>>>> Yeah, that's the problem with generic questions, instead of specific...
>>>>> "Talk is cheap."
>>>>>
>>>>> OK, so the hardware is exactly the same? Does FW bring any
>>>>> incompatibilities in the interface or is it just about the clocks? I
>>>>> guess I should not have included "with same FW" in my last statement.
>>>>> It's true, but way too narrow. Therefore let me rephrase it:
>>>>
>>>> HW is exactly the same. Let me give more insight on the setup. We have been
>>>> using the HW in virtual environment but now the ownership of certain
>>>> resources (e.g. clock controller etc.) is handed over to a different VM(non
>>>> Linux VM). Earlier the ownership of the resources was local to the same
>>>> VM(Linux VM) via passthrough mode so it could directly access them however
>>>> now Linux VM talks to non-Linux VM for its operations for resources that it
>>>> doesn't own anymore via some interface(shared memory/doorbell).  So shall we
>>>> use property like 'qcom, controlled-remotely' or do we need a new compatible
>>>> for such setup?
>>>>
>>>
>>> Krzysztof, just a ping on this thread.
>>>
>>> To summarise, the hardware is exactly same. We can consider the case of UFS. The
>>> UFS controller is exactly same in this proposed setup but the resources of the
>>> UFS controller are taken care by the VM. So instead of enabling the resources
>>> one by one, Linux kernel will just ask the VM to do so using an SCMI command.
>>>
>>> Due to this difference, we need to make the changes in the UFS controller
>>> driver. So we want to know if we can use a different compatible for the UFS
>>> controller altogether in DT (this will allow Linux kernel to have a separate
>>> driver and will simplify things) or just use a property like
>>> "remotely-controlled" to let the driver detect this setup and take action
>>> accordingly.
>>
>> What devices do we talk about? Are they released? For which other
>> devices you want to use it?
> 
> If you are referring to "peripherals" as "devices", then this new interface is
> going to be applicable to most of the peripherals in the SoC like PCIe, UFS, USB
> etc...
> 

And what about SoCs and final products?

Best regards,
Krzysztof