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

From: Sibi Sankar <quic_sibis@quicinc.com>
To: Konrad Dybcio <konrad.dybcio@linaro.org>, <sudeep.holla@arm.com>,
	<cristian.marussi@arm.com>, <andersson@kernel.org>,
	<jassisinghbrar@gmail.com>, <robh+dt@kernel.org>,
	<krzysztof.kozlowski+dt@linaro.org>
Cc: <linux-kernel@vger.kernel.org>, <linux-arm-msm@vger.kernel.org>,
	<devicetree@vger.kernel.org>, <quic_rgottimu@quicinc.com>,
	<quic_kshivnan@quicinc.com>, <conor+dt@kernel.org>,
	Amir Vajid <avajid@quicinc.com>
Subject: Re: [RFC 3/7] firmware: arm_scmi: Add QCOM vendor protocol
Date: Thu, 8 Feb 2024 17:14:58 +0530	[thread overview]
Message-ID: <2b1d9578-39cc-7836-a51b-be698bb50c43@quicinc.com> (raw)
In-Reply-To: <3325c6ea-ca30-40ee-83ba-c489dc9964b1@linaro.org>

On 1/18/24 01:45, Konrad Dybcio wrote:
> 
> 
> On 1/17/24 18:34, Sibi Sankar wrote:
>> From: Shivnandan Kumar <quic_kshivnan@quicinc.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.

> 
>>
>> Signed-off-by: Shivnandan Kumar <quic_kshivnan@quicinc.com>
>> Co-developed-by: Ramakrishna Gottimukkula <quic_rgottimu@quicinc.com>
>> Signed-off-by: Ramakrishna Gottimukkula <quic_rgottimu@quicinc.com>
>> Co-developed-by: Amir Vajid <avajid@quicinc.com>
>> Signed-off-by: Amir Vajid <avajid@quicinc.com>
>> Co-developed-by: Sibi Sankar <quic_sibis@quicinc.com>
>> Signed-off-by: Sibi Sankar <quic_sibis@quicinc.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. 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. 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.

> 
> That said, the spec (DEN0056C) says that protocol IDs 0x80-0xff
> are: "Reserved for vendor or platform-specific extensions to
> this interface.". So if perhaps there's a will to maintain
> multiple versions of this, with a way to discern between them..
> 
> Konrad
> 
> [1] 
> https://git.codelinaro.org/clo/la/kernel/msm-5.15/-/blob/KERNEL.PLATFORM.2.1.r5-05400-kernel.0/drivers/firmware/arm_scmi/memlat_vendor.c?ref_type=tags
> [2] 
> https://git.codelinaro.org/clo/la/kernel/msm-5.15/-/blob/KERNEL.PLATFORM.2.1.r5-05400-kernel.0/include/linux/scmi_memlat.h#L16