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

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Message-ID: <20190424064942.v5g6jr5l3xy5z3xv@vireshk-i7>
Date:   Wed, 24 Apr 2019 12:19:42 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Rajendra Nayak <rnayak@...eaurora.org>
Cc:     Georgi Djakov <georgi.djakov@...aro.org>, vireshk@...nel.org,
        sboyd@...nel.org, nm@...com, robh+dt@...nel.org,
        mark.rutland@....com, rjw@...ysocki.net, 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
Subject: Re: [PATCH v2 1/5] dt-bindings: opp: Introduce bandwidth-MBps
 bindings

On 24-04-19, 12:16, Rajendra Nayak wrote:
> 
> 
> On 4/23/2019 6:58 PM, Georgi Djakov wrote:
> > 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>;
> 
> Should this also have a bandwidth-MBps-name perhaps? Without that I guess we assume
> the order in which we specify the interconnects is the same as the order here?

Right, so I suggested not to add the -name property and to rely on the
order. Though I missed that he hasn't mentioned the order thing here.

@Georgi: Please mention above in the binding that the order is same as
interconnects binding.

-- 
viresh