Re: [Patch v4 01/10] dt-bindings: memory: tegra: add bpmp ref in tegra234-mc node

[Krzysztof Kozlowski]

On 28/03/2023 12:48, Thierry Reding wrote:
> On Tue, Mar 28, 2023 at 09:23:04AM +0200, Krzysztof Kozlowski wrote:
>> On 27/03/2023 18:14, Sumit Gupta wrote:
>>> For Tegra234, add the "nvidia,bpmp" property within the Memory
>>> Controller (MC) node to reference BPMP node. This is needed in
>>> the MC driver to pass the client info to the BPMP-FW when memory
>>> interconnect support is available.
>>>
>>> Signed-off-by: Sumit Gupta <sumitg@xxxxxxxxxx>
>>> ---
>>>  .../bindings/memory-controllers/nvidia,tegra186-mc.yaml    | 7 +++++++
>>>  1 file changed, 7 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra186-mc.yaml b/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra186-mc.yaml
>>> index 935d63d181d9..398d27bb2373 100644
>>> --- a/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra186-mc.yaml
>>> +++ b/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra186-mc.yaml
>>> @@ -58,6 +58,10 @@ properties:
>>>    "#interconnect-cells":
>>>      const: 1
>>>  
>>> +  nvidia,bpmp:
>>> +    $ref: /schemas/types.yaml#/definitions/phandle
>>> +    description: phandle of the node representing the BPMP
>>
>> Why do you need this multiple times? Both in parent and all external-mc
>> children?
> 
> We've had nvidia,bpmp in the external memory controller node since
> basically the beginning because we've always needed it there. For newer
> chips we now also need it for the memory controller.
> 
> Ideally I think we would only have this in the MC and have the EMC
> driver reference it via the EMC's parent (i.e. MC), but that would break
> backwards-compatibility. Reaching into the EMC's DT node from the MC was
> another option that we discussed internally, but it didn't look right
> given how this is also needed by the MC.
> 
> One thing we could potentially do is deprecate the nvidia,bpmp phandle
> in the EMC and only keep it as a fallback in the drivers in case the
> parent MC doesn't find it's own in the DT.

Yes, deprecation would answer to my question.

Best regards,
Krzysztof