linux-kernel - Re: [PATCH 0/3] opp: Add bw_factor support to adjust bandwidth dynamically

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Message-ID: <20250801072845.ppxka4ry4dtn6j3m@vireshk-i7>
Date: Fri, 1 Aug 2025 12:58:45 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Cc: Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
	Stephen Boyd <sboyd@...nel.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Manivannan Sadhasivam <mani@...nel.org>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kwilczynski@...nel.org>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 0/3] opp: Add bw_factor support to adjust bandwidth
 dynamically

On 01-08-25, 12:05, Krishna Chaitanya Chundru wrote:
> Can you please review this once.

Sorry about the delay.

> > The existing OPP table in the device tree for PCIe is shared across
> > different link configurations such as data rates 8GT/s x2 and 16GT/s x1.
> > These configurations often operate at the same frequency, allowing them
> > to reuse the same OPP entries. However, 8GT/s and 16 GT/s may have
> > different characteristics beyond frequency—such as RPMh votes in QCOM
> > case, which cannot be represented accurately when sharing a single OPP.

>From the looks of it, something like this should also work:

diff --git a/arch/arm64/boot/dts/qcom/sm8450.dtsi b/arch/arm64/boot/dts/qcom/sm8450.dtsi
index 54c6d0fdb2af..0a76bc4c4dc9 100644
--- a/arch/arm64/boot/dts/qcom/sm8450.dtsi
+++ b/arch/arm64/boot/dts/qcom/sm8450.dtsi
@@ -2216,18 +2216,12 @@ opp-2500000 {
                                        opp-peak-kBps = <250000 1>;
                                };

-                               /* GEN 1 x2 and GEN 2 x1 */
+                               /* 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>;
+                                       opp-peak-kBps-x1 = <500000 1>;
+                                       opp-peak-kBps-x2 = <1000000 1>;
                                };

                                /* GEN 3 x1 */
@@ -2237,18 +2231,12 @@ opp-8000000 {
                                        opp-peak-kBps = <984500 1>;
                                };

-                               /* GEN 3 x2 and GEN 4 x1 */
+                               /* GEN 4 x1 */
                                opp-16000000 {
                                        opp-hz = /bits/ 64 <16000000>;
                                        required-opps = <&rpmhpd_opp_nom>;
-                                       opp-peak-kBps = <1969000 1>;
-                               };
-
-                               /* GEN 4 x2 */
-                               opp-32000000 {
-                                       opp-hz = /bits/ 64 <32000000>;
-                                       required-opps = <&rpmhpd_opp_nom>;
-                                       opp-peak-kBps = <3938000 1>;
+                                       opp-peak-kBps-x1 = <1969000 1>;
+                                       opp-peak-kBps-x2 = <3938000 1>;
                                };
                        };

The OPP core supports named properties, which will make this work.

-- 
viresh