linux-kernel - Re: [PATCH 1/4] dt-bindings: opp: Introduce opp-bw-MBs bindings

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Message-ID: <e462c932-4789-4f59-ad58-98c62266d977@linaro.org>
Date:   Tue, 9 Apr 2019 17:36:01 +0300
From:   Georgi Djakov <georgi.djakov@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     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 1/4] dt-bindings: opp: Introduce opp-bw-MBs bindings

Hi Viresh,

On 3/14/19 08:23, Viresh Kumar wrote:
> On 13-03-19, 11:00, 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 | 45 +++++++++++++++++++
>>  1 file changed, 45 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/opp/opp.txt b/Documentation/devicetree/bindings/opp/opp.txt
>> index 76b6c79604a5..fa598264615f 100644
>> --- a/Documentation/devicetree/bindings/opp/opp.txt
>> +++ b/Documentation/devicetree/bindings/opp/opp.txt
>> @@ -129,6 +129,9 @@ Optional properties:
>>  - opp-microamp-<name>: Named opp-microamp property. Similar to
>>    opp-microvolt-<name> property, but for microamp instead.
>>  
>> +- opp-bw-MBs: The interconnect bandwidth is specified with an array containing
>> +  the two integer values for average and peak bandwidth in megabytes per second.
>> +
>>  - opp-level: A value representing the performance level of the device,
>>    expressed as a 32-bit integer.
>>  
>> @@ -546,3 +549,45 @@ Example 6: opp-microvolt-<name>, opp-microamp-<name>:
>>  		};
>>  	};
>>  };
>> +
>> +Example 7: opp-bw-MBs:
>> +(example: average and peak bandwidth values are defined for each OPP and the
>> +interconnect between CPU and DDR memory is scaled together with CPU frequency)
>> +
>> +/ {
>> +	cpus {
>> +		CPU0: cpu@0 {
>> +			compatible = "arm,cortex-a53", "arm,armv8";
>> +			...
>> +			operating-points-v2 = <&cpu_opp_table>;
>> +			/* path between the CPU and DDR memory */
>> +			interconnects = <&rpm_bimc MASTER_AMPSS_M0
>> +					&rpm_bimc SLAVE_EBI_CH0>;
> 
> Can we have multiple paths for a device ?

I suppose that this is also a possible scenario. Will propose something
to handle multiple paths too.

>> +		};
>> +	};
>> +
>> +	cpu_opp_table: cpu_opp_table {
>> +		compatible = "operating-points-v2";
>> +		opp-shared;
>> +
>> +		opp-200000000 {
>> +			opp-hz = /bits/ 64 <200000000>;
>> +			/* 457 MB/s average and 1525 MB/s peak bandwidth */
>> +			opp-bw-MBs = <457 1525>;
> 
> In that case fixing this to just 2 entries in the array is incorrect
> and we should take care of that in the bindings here.

We can encode the path name into the property (when there are multiple
paths). We already have opp-microamp-<name> and opp-microamp-<name>, so
we can follow the same practice.

For example:

CPU0: cpu@0 {
	compatible = "arm,cortex-a53", "arm,armv8";
	...
	operating-points-v2 = <&cpu_opp_table>;
	/* path between the CPU and DDR and path between CPU and L3 */
	interconnects = <&bimc MASTER_AMPSS_M0 &bimc SLAVE_EBI_CH0>,
			<&bimc MASTER_AMPSS_M0 &bimc SLAVE_L3>;
	interconnect-names "cpu-mem", "cpu-l3";
};

cpu_opp_table: cpu_opp_table {
	compatible = "operating-points-v2";
	opp-shared;

	opp-200000000 {
		opp-hz = /bits/ 64 <200000000>;
		/* 457 MB/s average, 1525 MB/s peak bandwidth to DDR */
		opp-bw-MBps-cpu-mem = <457 1525>;
		/* 914 MB/s average, 3050 MB/s peak bandwidth to L3 */
		opp-bw-MBps-cpu-l3 = <914 3050>;
	};
};

Thanks,
Georgi