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

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Date:   Sun, 2 Apr 2023 12:47:01 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Sumit Gupta <sumitg@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>
Cc:     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 29/03/2023 19:12, Sumit Gupta wrote:
> 
> 
> On 28/03/23 18:18, Thierry Reding wrote:
>> On Tue, Mar 28, 2023 at 01:22:26PM +0200, Krzysztof Kozlowski wrote:
>>> 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.
>>
>> Okay, great. Sumit, you can resolve this by adding a "deprecated: true"
>> to the EMC's nvidia,bpmp property schema. In the driver we can then try
>> to look at the MC's ->bpmp and if it exists reuse that. If it doesn't
>> exist, we can keep the existing lookup as a fallback for device trees
>> that haven't been updated yet.
> 
> We can't use MC's->bpmp in the EMC driver's probe as it will be NULL. 
> This is because MC driver uses "arch_initcall" and gets probed earlier 
> than BPMP. We can do this in another way as below change. This way we 
> can use the existing "nvidia,bpmp" property from EMC node and don't need 
> to move it to the MC node. Please share if this change sounds OK.

Then rather it sounds like time to fix these
orderings/arch_initcall/missing defer.


Best regards,
Krzysztof