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

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Date:   Wed, 24 Apr 2019 21:24:50 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Sibi Sankar <sibis@...eaurora.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        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, amit.kucheria@...aro.org,
        seansw@....qualcomm.com, daidavid1@...eaurora.org,
        evgreen@...omium.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 Wed 24 Apr 02:00 PDT 2019, Sibi Sankar wrote:
> On 4/24/19 12:19 PM, Viresh Kumar wrote:
> > On 24-04-19, 12:16, Rajendra Nayak wrote:
> > > On 4/23/2019 6:58 PM, Georgi Djakov wrote:
[..]
> > > > +/ {
> > > > +	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.
> 
> by skipping names, aren't we forced to specify all the specified paths
> bandwidths for each opp even if it is redundant? i.e if the first/second
> icc path doesn't have to change across a few opps but if the other path
> does need to change this scheme would force it to be included and will
> try to set the first/second path again.
> 
> 
> e.g: Here the first path does not have to change across these two opps
> but have to specified nonetheless since we omit names.
> 

If this is a pair in the middle of the list, we would either have to
define how non-specified values are inherited from neighbouring nodes or
you will get different behavior if you're coming from a lower or a
higher opp.

I think it looks clearer to just be explicit and repeat the values.

Regards,
Bjorn

> +		opp-1200000000 {
> +			opp-hz = /bits/ 64 <1200000000>;
> +			bandwidth-MBps = <457 1525>, <914 3050>;
> +		};
> +		opp-1400000000 {
> +			opp-hz = /bits/ 64 <1400000000>;
> +			bandwidth-MBps = <457 1525>, <1828 6102>;
> +		};