linux-kernel - Re: [RFC 3/7] firmware: arm_scmi: Add QCOM vendor protocol

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Message-ID: <de2b3cd3-95f9-4fc4-4d51-35be32a788e9@quicinc.com>
Date: Mon, 12 Feb 2024 14:26:05 +0530
From: Sibi Sankar <quic_sibis@...cinc.com>
To: Konrad Dybcio <konrad.dybcio@...aro.org>, <sudeep.holla@....com>,
        <cristian.marussi@....com>, <andersson@...nel.org>,
        <jassisinghbrar@...il.com>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>
CC: <linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <quic_rgottimu@...cinc.com>,
        <quic_kshivnan@...cinc.com>, <conor+dt@...nel.org>,
        Amir Vajid
	<avajid@...cinc.com>
Subject: Re: [RFC 3/7] firmware: arm_scmi: Add QCOM vendor protocol



On 2/10/24 04:15, Konrad Dybcio wrote:
> On 8.02.2024 12:44, Sibi Sankar wrote:
>>
>>
>> On 1/18/24 01:45, Konrad Dybcio wrote:
>>>
>>>
>>> On 1/17/24 18:34, Sibi Sankar wrote:
>>>> From: Shivnandan Kumar <quic_kshivnan@...cinc.com>
>>>>
>>>> SCMI QCOM vendor protocol provides interface to communicate with SCMI
>>>> controller and enable vendor specific features like bus scaling capable
>>>> of running on it.
>>>
>>
>> Hey Konrad,
>>
>>> "QCOM protocol" sounds overly generic, especially given how many
>>> different vendor protocols have historically been present in
>>> QC firmware..
>>
>> Here it is specifically mentioned that way to communicate that
>> this is the only vendor protocol exposed by Qualcomm. It handles
>> all the other protocols which were usually handled separately on
>> older SoCs.
> 
> I'm no SCMI specialist but that's a rather.. peculiar design decision,
> I guess
> 
> 
>>
>>>
>>>>
>>>> Signed-off-by: Shivnandan Kumar <quic_kshivnan@...cinc.com>
>>>> Co-developed-by: Ramakrishna Gottimukkula <quic_rgottimu@...cinc.com>
>>>> Signed-off-by: Ramakrishna Gottimukkula <quic_rgottimu@...cinc.com>
>>>> Co-developed-by: Amir Vajid <avajid@...cinc.com>
>>>> Signed-off-by: Amir Vajid <avajid@...cinc.com>
>>>> Co-developed-by: Sibi Sankar <quic_sibis@...cinc.com>
>>>> Signed-off-by: Sibi Sankar <quic_sibis@...cinc.com>
>>>> ---
>>>
>>> So, this is another 0x80 protocol, different to the one that has
>>> been shipping on devices that got released with msm-5.4, msm-5.10
>>> and msm-5.15 [1][2]. They're totally incompatible (judging by the
>>> msg format), use the same protocol ID and they are (at a glance)
>>> providing access to the same HW/FW/tunables.
>>
>> Thanks for bringing this up but like I already explained the only
>> SoC that was actually shipped with ^^ protocol was SC7180 and we
>> already have an alternative arrangement for memory dvfs upstreamed
>> on it.
> 
> Ok, that makes sense.
> 
> I took my 8550 phone, enabled some debug prints and it looks like the
> only SCMI protocol exposed is 0x19 (which doesn't seem to be defined).
> 
> Not sure what other devices would spit out, but I assume what you said
> is true.
> 
> For completeness, the reported rev is:
> 
> arm-scmi firmware:scmi: SCMI Protocol v2.0 'Qualcomm:' Firmware version 0x10000
> 
>> Further more it handles only L3 dvfs so it makes zero sense
>> to try to upstream the older protocol given that working dvfs solution
>> already exists upstream.
> 
> We don't have any sort of governor for it though, so I wouldn't go as
> far as calling it working :P

It is a working solution (it is equivalent to the compute mon mapping in
downstream implementation) but isn't feature complete ¯\_(ツ)_/¯.

> 
>> All other SoCs don't have the 0x80 protocol
>> enabled for memory dvfs in production.
>>
>>>
>>> I'm not sure if this can be trusted not to change again.. Unless
>>> we get a strong commitment that all platforms (compute, mobile,
>>> auto, iot, whatever) stick to this one..
>>
>> This is exactly that consolidation effort from Qualcomm. Here they
>> expose just one vendor protocol and implement all the algorithms just
>> through it.
> 
> And I'm very glad you're taking such consolidation steps.. Just a little
> worried that in case this protocol's extensibility is exhausted, the next
> one would need to be called.. "Qualcomm2"?

We don't see ^^ happening in the near future (meaning this doesn't apply
to just X1E). The consolidation would still be better than spinning out
n number of protocols per SoC.

-Sibi

> 
> Konrad