linux-kernel - Re: [PATCH 2/3] arm64: dts: qcom: sa8775p: Add CPU OPP tables to scale DDR/L3

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Message-ID: <daqa3krsp6emdha6h7tlcelsggb6qeilnojgtfxjbp5zw4n6ow@xzwdmu55ygjf>
Date: Fri, 15 Nov 2024 00:48:55 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Jagadeesh Kona <quic_jkona@...cinc.com>
Cc: Brian Masney <bmasney@...hat.com>, 
	Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konradybcio@...nel.org>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Ajit Pandey <quic_ajipan@...cinc.com>, 
	Imran Shaik <quic_imrashai@...cinc.com>, Taniya Das <quic_tdas@...cinc.com>, 
	Satya Priya Kakitapalli <quic_skakitap@...cinc.com>, Shivnandan Kumar <quic_kshivnan@...cinc.com>
Subject: Re: [PATCH 2/3] arm64: dts: qcom: sa8775p: Add CPU OPP tables to
 scale DDR/L3

On Mon, Nov 11, 2024 at 06:39:48PM +0530, Jagadeesh Kona wrote:
> 
> 
> On 10/17/2024 9:12 PM, Brian Masney wrote:
> > On Thu, Oct 17, 2024 at 02:58:31PM +0530, Jagadeesh Kona wrote:
> >> +	cpu0_opp_table: opp-table-cpu0 {
> >> +		compatible = "operating-points-v2";
> >> +		opp-shared;
> >> +
> >> +		cpu0_opp_1267mhz: opp-1267200000 {
> >> +			opp-hz = /bits/ 64 <1267200000>;
> >> +			opp-peak-kBps = <6220800 29491200>;
> >> +		};
> >> +
> >> +		cpu0_opp_1363mhz: opp-1363200000 {
> >> +			opp-hz = /bits/ 64 <1363200000>;
> >> +			opp-peak-kBps = <6220800 29491200>;
> >> +		};
> > 
> > [snip]
> > 
> >> +	cpu4_opp_table: opp-table-cpu4 {
> >> +		compatible = "operating-points-v2";
> >> +		opp-shared;
> >> +
> >> +		cpu4_opp_1267mhz: opp-1267200000 {
> >> +			opp-hz = /bits/ 64 <1267200000>;
> >> +			opp-peak-kBps = <6220800 29491200>;
> >> +		};
> >> +
> >> +		cpu4_opp_1363mhz: opp-1363200000 {
> >> +			opp-hz = /bits/ 64 <1363200000>;
> >> +			opp-peak-kBps = <6220800 29491200>;
> >> +		};
> > 
> > There's no functional differences in the cpu0 and cpu4 opp tables. Can
> > a single table be used?
> > 
> > This aligns with my recollection that this particular SoC only has the
> > gold cores.
> > 
> > Brian
> > 
> 
> Thanks Brian for your review. Sorry for the delayed response.
> 
> We require separate OPP tables for CPU0 and CPU4 to allow independent
> scaling of DDR and L3 frequencies for each CPU domain, with the final
> DDR and L3 frequencies being an aggregate of both.
> 
> If we use a single OPP table for both CPU domains, then _allocate_opp_table() [1]
> won't be invoked for CPU4. As a result both CPU devices will end up in sharing
> the same ICC path handle, which could lead to one CPU device overwriting the bandwidth
> votes of other.

All of this should be a part of the commit message.

> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/opp/core.c#n1588
> 
> Thanks,
> Jagadeesh
>  

-- 
With best wishes
Dmitry