linux-kernel - Re: [PATCH 2/2] arm64: dts: qcom: sc7280: Add cpu OPP tables

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Message-ID: <1fc9fb8d9a94909ff9b7b76d598bd266@codeaurora.org>
Date:   Tue, 04 May 2021 23:55:10 +0530
From:   Sibi Sankar <sibis@...eaurora.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     bjorn.andersson@...aro.org, viresh.kumar@...aro.org,
        swboyd@...omium.org, agross@...nel.org, robh+dt@...nel.org,
        rjw@...ysocki.net, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, dianders@...omium.org, mka@...omium.org
Subject: Re: [PATCH 2/2] arm64: dts: qcom: sc7280: Add cpu OPP tables

Hey Sudeep,

Thanks for the review!

On 2021-05-04 20:12, Sudeep Holla wrote:
> On Fri, Apr 30, 2021 at 07:58:21PM +0530, Sibi Sankar wrote:
>> Add OPP tables required to scale DDR/L3 per freq-domain on SC7280 
>> SoCs.
>> 
>> Signed-off-by: Sibi Sankar <sibis@...eaurora.org>
>> ---
>>  arch/arm64/boot/dts/qcom/sc7280.dtsi | 135 
>> +++++++++++++++++++++++++++++++++++
>>  1 file changed, 135 insertions(+)
>> 
>> diff --git a/arch/arm64/boot/dts/qcom/sc7280.dtsi 
>> b/arch/arm64/boot/dts/qcom/sc7280.dtsi
>> index 0bb835aeae33..90220cecb368 100644
>> --- a/arch/arm64/boot/dts/qcom/sc7280.dtsi
>> +++ b/arch/arm64/boot/dts/qcom/sc7280.dtsi
> 
> 
> [...]
> 
>> @@ -248,6 +273,116 @@
>>  		};
>>  	};
>> 
>> +	cpu0_opp_table: cpu0_opp_table {
>> +		compatible = "operating-points-v2";
>> +		opp-shared;
>> +
>> +		cpu0_opp1: opp-300000000 {
>> +			opp-hz = /bits/ 64 <300000000>;
>> +			opp-peak-kBps = <800000 9600000>;
>> +		};
>> +
>> +		cpu0_opp2: opp-691200000 {
>> +			opp-hz = /bits/ 64 <691200000>;
>> +			opp-peak-kBps = <800000 17817600>;
>> +		};
>> +
>> +		cpu0_opp3: opp-806400000 {
>> +			opp-hz = /bits/ 64 <806400000>;
>> +			opp-peak-kBps = <800000 20889600>;
>> +		};
>> +
>> +		cpu0_opp4: opp-940800000 {
>> +			opp-hz = /bits/ 64 <940800000>;
>> +			opp-peak-kBps = <1804000 24576000>;
>> +		};
>> +
>> +		cpu0_opp5: opp-1152000000 {
>> +			opp-hz = /bits/ 64 <1152000000>;
>> +			opp-peak-kBps = <2188000 27033600>;
>> +		};
>> +
>> +		cpu0_opp6: opp-1324800000 {
>> +			opp-hz = /bits/ 64 <1324800000>;
>> +			opp-peak-kBps = <2188000 33792000>;
>> +		};
>> +
>> +		cpu0_opp7: opp-1516800000 {
>> +			opp-hz = /bits/ 64 <1516800000>;
>> +			opp-peak-kBps = <3072000 38092800>;
>> +		};
>> +
>> +		cpu0_opp8: opp-1651200000 {
>> +			opp-hz = /bits/ 64 <1651200000>;
>> +			opp-peak-kBps = <3072000 41779200>;
>> +		};
>> +
>> +		cpu0_opp9: opp-1804800000 {
>> +			opp-hz = /bits/ 64 <1804800000>;
>> +			opp-peak-kBps = <4068000 48537600>;
>> +		};
>> +
>> +		cpu0_opp10: opp-1958400000 {
>> +			opp-hz = /bits/ 64 <1958400000>;
>> +			opp-peak-kBps = <4068000 48537600>;
>> +		};
>> +	};
>> +
> 
> NACK, this breaks if there is a mismatch from what is read from the 
> hardware
> and what is presented in this table above. Either add it from the some
> bootloader or other boot code to this table reading from the 
> hardware/firmware
> or find a way to link them without this.
> 
> Sorry I had warned long back about this when such links were discussed 
> as
> part of interconnect binding.

Not sure why this warrants a NACK,
as this was consensus for mapping
cpu freq to DDR/L3 bandwidth votes.
(We use the same solution on SDM845
and SC7180). The opp tables are
optional and when specified puts in
votes for DDR/L3. In the future the
table can be safely dropped when more
useful devfreq governors are upstreamed.

cpufreq: qcom: Don't add frequencies without an OPP

I guess your main concern for breakage
is ^^ commit? The original design is
to list a super set of frequencies
supported by all variants of the SoC
along with the required DDR/L3 bandwidth
values. When we run into non-documented
frequency we just wouldn't put in bw
votes for it which should be fine since
the entire opp_table is optional. If
this is the reason for the NACK I can
try get it reverted with Matthias's ack.


-- 
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