Re: [PATCH v1 08/16] arm64: dts: mt8195: Add power domains controller

[Krzysztof Kozlowski]

On 06/07/2022 15:41, Matthias Brugger wrote:
> 
> 
> On 04/07/2022 14:38, Krzysztof Kozlowski wrote:
>> On 04/07/2022 12:00, Tinghan Shen wrote:
>>> Add power domains controller node for mt8195.
>>>
>>> Signed-off-by: Weiyi Lu <weiyi.lu@xxxxxxxxxxxx>
>>> Signed-off-by: Tinghan Shen <tinghan.shen@xxxxxxxxxxxx>
>>> ---
>>>   arch/arm64/boot/dts/mediatek/mt8195.dtsi | 327 +++++++++++++++++++++++
>>>   1 file changed, 327 insertions(+)
>>>
>>> diff --git a/arch/arm64/boot/dts/mediatek/mt8195.dtsi b/arch/arm64/boot/dts/mediatek/mt8195.dtsi
>>> index 8d59a7da3271..d52e140d9271 100644
>>> --- a/arch/arm64/boot/dts/mediatek/mt8195.dtsi
>>> +++ b/arch/arm64/boot/dts/mediatek/mt8195.dtsi
>>> @@ -10,6 +10,7 @@
>>>   #include <dt-bindings/interrupt-controller/irq.h>
>>>   #include <dt-bindings/phy/phy.h>
>>>   #include <dt-bindings/pinctrl/mt8195-pinfunc.h>
>>> +#include <dt-bindings/power/mt8195-power.h>
>>>   
>>>   / {
>>>   	compatible = "mediatek,mt8195";
>>> @@ -338,6 +339,332 @@
>>>   			#interrupt-cells = <2>;
>>>   		};
>>>   
>>> +		scpsys: syscon@10006000 {
>>> +			compatible = "syscon", "simple-mfd";
>>
>> These compatibles cannot be alone.
>>
> 
> You mean we would need something like "mediatek,scpsys" as dummy compatible 
> that's not bound to any driver?

Yes. syscon (and simple-mfd) must always come with a specific compatible.

> 
>>> +			reg = <0 0x10006000 0 0x1000>;
>>> +			#power-domain-cells = <1>;
>>
>> If it is simple MFD, then probably it is not a power domain provider.
>> Decide.
> 
> The SCPSYS IP block of MediaTek SoCs group several functionality, one is the 
> power domain controller. Others are not yet implemented, but defining the scpsys 
> as a MFD will give us the possibility to do so in the future.

No, quite the opposite. Having simple-mfd prevents you from implementing
it correctly later as a driver, because you cannot remove it. It would
be ABI break.

It's fine to have one block being a simple MFD having several children,
but then it's not a power controller. Children could be such power
controller, but not simple-mfd. Rob explained this several times:
https://lore.kernel.org/all/YXhINE00HG6hbQI4@xxxxxxxxxxxxxxxxxx/
https://lore.kernel.org/all/20220701000959.GA3588170-robh@xxxxxxxxxx/


Best regards,
Krzysztof