linux-kernel - Re: [PATCH v10 4/6] arm64: dts: qcom: sm8450: Add OPP table support to PCIe

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Message-ID: <aaee8605-848f-fe9c-63aa-af4ae2d399a6@quicinc.com>
Date: Mon, 22 Apr 2024 22:25:06 +0530
From: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
CC: Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio
	<konrad.dybcio@...aro.org>,
        Rob Herring <robh@...nel.org>,
        "Krzysztof
 Kozlowski" <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley
	<conor+dt@...nel.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas
	<bhelgaas@...gle.com>, <johan+linaro@...nel.org>,
        <bmasney@...hat.com>, <djakov@...nel.org>,
        <linux-arm-msm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <vireshk@...nel.org>, <quic_vbadigan@...cinc.com>,
        <quic_skananth@...cinc.com>, <quic_nitegupt@...cinc.com>,
        <quic_parass@...cinc.com>, <krzysztof.kozlowski@...aro.org>
Subject: Re: [PATCH v10 4/6] arm64: dts: qcom: sm8450: Add OPP table support
 to PCIe



On 4/22/2024 8:14 PM, Manivannan Sadhasivam wrote:
> On Tue, Apr 09, 2024 at 03:43:22PM +0530, Krishna chaitanya chundru wrote:
>> PCIe needs to choose the appropriate performance state of RPMh power
> 
> 'PCIe host controller driver'
> 
>> domain and interconnect bandwidth based up on the PCIe data rate.
> 
> 'based on the PCIe data rate'
> 
>>
>> Add the OPP table support to specify RPMh performance states and
> 
> 'Hence, add...'
> 
>> interconnect peak bandwidth.
>>
>> Different link configurations may share the same aggregate bandwidth,
> 
> 'It should be noted that the different...'
> 
>> e.g., a 2.5 GT/s x2 link and a 5.0 GT/s x1 link have the same bandwidth
>> and share the same OPP entry.
>>
>> Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>
>> ---
>>   arch/arm64/boot/dts/qcom/sm8450.dtsi | 77 ++++++++++++++++++++++++++++++++++++
>>   1 file changed, 77 insertions(+)
>>
>> diff --git a/arch/arm64/boot/dts/qcom/sm8450.dtsi b/arch/arm64/boot/dts/qcom/sm8450.dtsi
>> index 615296e13c43..9dfe16012726 100644
>> --- a/arch/arm64/boot/dts/qcom/sm8450.dtsi
>> +++ b/arch/arm64/boot/dts/qcom/sm8450.dtsi
>> @@ -1855,7 +1855,35 @@ &mc_virt SLAVE_EBI1 QCOM_ICC_TAG_ALWAYS>,
>>   			pinctrl-names = "default";
>>   			pinctrl-0 = <&pcie0_default_state>;
>>   
>> +			operating-points-v2 = <&pcie0_opp_table>;
>> +
>>   			status = "disabled";
>> +
>> +			pcie0_opp_table: opp-table {
>> +				compatible = "operating-points-v2";
>> +
>> +				/* GEN 1 x1 */
>> +				opp-2500000 {
>> +					opp-hz = /bits/ 64 <2500000>;
>> +					required-opps = <&rpmhpd_opp_low_svs>;
>> +					opp-peak-kBps = <250000 1>;
>> +				};
>> +
>> +				/* GEN 2 x1 */
>> +				opp-5000000 {
>> +					opp-hz = /bits/ 64 <5000000>;
>> +					required-opps = <&rpmhpd_opp_low_svs>;
>> +					opp-peak-kBps = <500000 1>;
>> +				};
>> +
>> +				/* GEN 3 x1 */
>> +				opp-8000000 {
>> +					opp-hz = /bits/ 64 <8000000>;
> 
> I doubt this value. See below...
> 
>> +					required-opps = <&rpmhpd_opp_nom>;
>> +					opp-peak-kBps = <984500 1>;
>> +				};
>> +			};
>> +
>>   		};
>>   
>>   		pcie0_phy: phy@...6000 {
>> @@ -1982,7 +2010,56 @@ &mc_virt SLAVE_EBI1 QCOM_ICC_TAG_ALWAYS>,
>>   			pinctrl-names = "default";
>>   			pinctrl-0 = <&pcie1_default_state>;
>>   
>> +			operating-points-v2 = <&pcie1_opp_table>;
>> +
>>   			status = "disabled";
>> +
>> +			pcie1_opp_table: opp-table {
>> +				compatible = "operating-points-v2";
>> +
>> +				/* GEN 1 x1 */
>> +				opp-2500000 {
>> +					opp-hz = /bits/ 64 <2500000>;
>> +					required-opps = <&rpmhpd_opp_low_svs>;
>> +					opp-peak-kBps = <250000 1>;
>> +				};
>> +
>> +				/* GEN 1 x2 GEN 2 x1 */
>> +				opp-5000000 {
>> +					opp-hz = /bits/ 64 <5000000>;
>> +					required-opps = <&rpmhpd_opp_low_svs>;
>> +					opp-peak-kBps = <500000 1>;
>> +				};
>> +
>> +				/* GEN 2 x2 */
>> +				opp-10000000 {
>> +					opp-hz = /bits/ 64 <10000000>;
>> +					required-opps = <&rpmhpd_opp_low_svs>;
>> +					opp-peak-kBps = <1000000 1>;
>> +				};
>> +
>> +				/* GEN 3 x1 */
>> +				opp-8000000 {
>> +					opp-hz = /bits/ 64 <8000000>;
> 
> GEN 3 x1 frequency is lower than GEN 2 x2? This looks strange. Both should be of
> same frequency.
> 
Gen2 is 5GT/s where as GEN3 is 8GT/s. so the freq for 3 x1(8 x1 GT/s) is
less than Gen2 x2(5 x2 GT/s)

- Krishna Chaitanya.
>> +					required-opps = <&rpmhpd_opp_nom>;
>> +					opp-peak-kBps = <984500 1>;
>> +				};
>> +
>> +				/* GEN 3 x2 GEN 4 x1 */
> 
> 'GEN 3 x2 and GEN 4 x1'
> 
> - Mani
>