linux-kernel - Re: [PATCH v5 1/2] dt-bindings: arm: Add new compatible for smc/hvc transport for SCMI

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Message-ID: <0a039a5a-46c8-4f63-a9e4-fd5b197340ab@linaro.org>
Date:   Mon, 9 Oct 2023 23:03:45 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Nikunj Kela <quic_nkela@...cinc.com>,
        Sudeep Holla <sudeep.holla@....com>
Cc:     cristian.marussi@....com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        andersson@...nel.org, linux-arm-kernel@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v5 1/2] dt-bindings: arm: Add new compatible for smc/hvc
 transport for SCMI



On 10/9/23 16:52, Nikunj Kela wrote:
> 
> On 10/9/2023 7:41 AM, Sudeep Holla wrote:
>> On Fri, Oct 06, 2023 at 09:42:05AM -0700, Nikunj Kela wrote:
>>> Introduce compatible "qcom,scmi-smc" for SCMI smc/hvc transport 
>>> channel for
>>> Qualcomm virtual platforms.
>>>
>>> This compatible mandates populating an additional parameter 
>>> 'capability-id'
>>> from the last 8 bytes of the shmem channel.
>>>
>> While I am happy with the simplification here, I am also bit nervous how
>> long before Qualcomm abandons this. I hope this is adopted as is in all
>> internal and downstream code without any modifications and this is not
>> just a push for upstreaming some change to minimise delta with internal/
>> downstream code.
>>
>> -- 
>> Regards,
>> Sudeep
> 
> Qualcomm is using patch on all the virtual auto platforms using 
> shmem/doorbell as scmi channel. This is already being used without any 
> modifications in our downstream code. No delta for this patch series. 
> Thanks!
AFAICT Sudeep is looking for a solid guarantee that it will continue to 
be used as-is, on more than one platform and on more than one BSP version.

There have been cases where such firmware interfaces had silent ABI 
breaks (or were replaced altogether) between qc downstream branches and 
this would be unacceptable. Understandably, having a unified means of 
communication for *all* Qualcomm chips (i.e. not only auto) going 
forward would likely be expected..

Konrad