linux-kernel - [PATCH v2 1/5] dt-bindings: opp: Introduce bandwidth-MBps bindings

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Date:   Tue, 23 Apr 2019 16:28:19 +0300
From:   Georgi Djakov <georgi.djakov@...aro.org>
To:     vireshk@...nel.org, sboyd@...nel.org, nm@...com,
        robh+dt@...nel.org, mark.rutland@....com, rjw@...ysocki.net
Cc:     jcrouse@...eaurora.org, vincent.guittot@...aro.org,
        bjorn.andersson@...aro.org, amit.kucheria@...aro.org,
        seansw@....qualcomm.com, daidavid1@...eaurora.org,
        evgreen@...omium.org, sibis@...eaurora.org,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        georgi.djakov@...aro.org
Subject: [PATCH v2 1/5] dt-bindings: opp: Introduce bandwidth-MBps bindings

In addition to frequency and voltage, some devices may have bandwidth
requirements for their interconnect throughput - for example a CPU
or GPU may also need to increase or decrease their bandwidth to DDR
memory based on the current operating performance point.

Extend the OPP tables with additional property to describe the bandwidth
needs of a device. The average and peak bandwidth values depend on the
hardware and its properties.

Signed-off-by: Georgi Djakov <georgi.djakov@...aro.org>
---
 Documentation/devicetree/bindings/opp/opp.txt | 38 +++++++++++++++++++
 .../devicetree/bindings/property-units.txt    |  4 ++
 2 files changed, 42 insertions(+)

diff --git a/Documentation/devicetree/bindings/opp/opp.txt b/Documentation/devicetree/bindings/opp/opp.txt
index 76b6c79604a5..830f0206aea7 100644
--- a/Documentation/devicetree/bindings/opp/opp.txt
+++ b/Documentation/devicetree/bindings/opp/opp.txt
@@ -132,6 +132,9 @@ Optional properties:
 - opp-level: A value representing the performance level of the device,
   expressed as a 32-bit integer.
 
+- bandwidth-MBps: The interconnect bandwidth is specified with an array containing
+  the two integer values for average and peak bandwidth in megabytes per second.
+
 - clock-latency-ns: Specifies the maximum possible transition latency (in
   nanoseconds) for switching to this OPP from any other OPP.
 
@@ -546,3 +549,38 @@ Example 6: opp-microvolt-<name>, opp-microamp-<name>:
 		};
 	};
 };
+
+Example 7: bandwidth-MBps:
+Average and peak bandwidth values for the interconnects between CPU and DDR
+memory and also between CPU and L3 are defined per each OPP. Bandwidth of both
+interconnects is scaled together with CPU frequency.
+
+/ {
+	cpus {
+		CPU0: cpu@0 {
+			compatible = "arm,cortex-a53", "arm,armv8";
+			...
+			operating-points-v2 = <&cpu_opp_table>;
+			/* path between CPU and DDR memory and CPU and L3 */
+			interconnects = <&noc MASTER_CPU &noc SLAVE_DDR>,
+					<&noc MASTER_CPU &noc SLAVE_L3>;
+		};
+	};
+
+	cpu_opp_table: cpu_opp_table {
+		compatible = "operating-points-v2";
+		opp-shared;
+
+		opp-200000000 {
+			opp-hz = /bits/ 64 <200000000>;
+			/* CPU<->DDR bandwidth: 457 MB/s average, 1525 MB/s peak */
+			 * CPU<->L3 bandwidth: 914 MB/s average, 3050 MB/s peak */
+			bandwidth-MBps = <457 1525>, <914 3050>;
+		};
+		opp-400000000 {
+			opp-hz = /bits/ 64 <400000000>;
+			/* CPU<->DDR bandwidth: 915 MB/s average, 3051 MB/s peak */
+			 * CPU<->L3 bandwidth: 1828 MB/s average, 6102 MB/s peak */
+			bandwidth-MBps = <915 3051>, <1828 6102>;
+		};
+	};
diff --git a/Documentation/devicetree/bindings/property-units.txt b/Documentation/devicetree/bindings/property-units.txt
index bfd33734faca..9c3dbefcdae8 100644
--- a/Documentation/devicetree/bindings/property-units.txt
+++ b/Documentation/devicetree/bindings/property-units.txt
@@ -41,3 +41,7 @@ Temperature
 Pressure
 ----------------------------------------
 -kpascal	: kiloPascal
+
+Throughput
+----------------------------------------
+-MBps		: megabytes per second