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

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Date:   Tue, 28 Mar 2023 13:22:26 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Sumit Gupta <sumitg@...dia.com>, treding@...dia.com,
        dmitry.osipenko@...labora.com, viresh.kumar@...aro.org,
        rafael@...nel.org, jonathanh@...dia.com, robh+dt@...nel.org,
        lpieralisi@...nel.org, linux-kernel@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-pci@...r.kernel.org,
        mmaddireddy@...dia.com, kw@...ux.com, bhelgaas@...gle.com,
        vidyas@...dia.com, sanjayc@...dia.com, ksitaraman@...dia.com,
        ishah@...dia.com, bbasu@...dia.com
Subject: Re: [Patch v4 01/10] dt-bindings: memory: tegra: add bpmp ref in
 tegra234-mc node

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@...dia.com>
>>> ---
>>>  .../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