linux-kernel - RE: Re: [PATCH V4 4/5] soc: qcom: Introduce SCMI based Memlat (Memory Latency) governor

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Message-ID: <20241115003809epcms1p518df149458f3023d33ec6d87a315e8f6@epcms1p5>
Date: Fri, 15 Nov 2024 09:38:09 +0900
From: MyungJoo Ham <myungjoo.ham@...sung.com>
To: Sibi Sankar <quic_sibis@...cinc.com>, Dmitry Baryshkov
	<dmitry.baryshkov@...aro.org>, Kyungmin Park <Kyungmin.park@...sung.com>,
	Chanwoo Choi <cw00.choi@...sung.com>, Viresh Kumar <viresh.kumar@...aro.org>
CC: "sudeep.holla@....com" <sudeep.holla@....com>,
	"cristian.marussi@....com" <cristian.marussi@....com>,
	"andersson@...nel.org" <andersson@...nel.org>, "konrad.dybcio@...aro.org"
	<konrad.dybcio@...aro.org>, "robh+dt@...nel.org" <robh+dt@...nel.org>,
	"krzysztof.kozlowski+dt@...aro.org" <krzysztof.kozlowski+dt@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "quic_rgottimu@...cinc.com"
	<quic_rgottimu@...cinc.com>, "quic_kshivnan@...cinc.com"
	<quic_kshivnan@...cinc.com>, "conor+dt@...nel.org" <conor+dt@...nel.org>,
	"arm-scmi@...r.kernel.org" <arm-scmi@...r.kernel.org>, Amir Vajid
	<avajid@...cinc.com>
Subject: RE: Re: [PATCH V4 4/5] soc: qcom: Introduce SCMI based Memlat
 (Memory Latency) governor

>
>Hey Dmitry,
>
>Thanks for taking time to review the series.
>
>+ Devfreq maintainers to comment (I thought you already added
>them by name)
>
>
>Hey MyungJoo/Kyungmin/Chanwoo,
>
>Can you weigh in here? Does it make sense to add a new
>class of devfreq devices that don't have governors
>associated with them just for them to export a few
>essential data to userspace? In this scenario the
>scaling algorithm is in a SCP and we just start
>them from the kernel. We do have ways to get the
>current frequency of various buses but does this
>warrant adding a new class of governor less devices?
>
>-Sibi

If voltage/frequency is controlled by SCP
(it's an SoC's internal hardware IP, right?),
it's good to have a userspace governer
with the driver not accepting updates from userspace.

E.g., Let "target" callback not update the frequency value,
 or let "target" callback always return an error with
 a dev_err message that you don't accept frequency changes
 from userspace.

Cheers,
MyungJoo.