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

Rob Herring
2019-03-28T15:12:55Z

On Wed, Mar 13, 2019 at 11:00:07AM +0200, 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.

How would this work if you have 1 OPP (for the bus/interconnect/ddr) and
2 devices with variable bandwidth needs? Or 'device' here means the
interconnect?

>
> Signed-off-by: Georgi Djakov <georgi.djakov@linaro.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.

-MBps would be better IMO. Either way, units should be documented in
property-units.txt.

> +
> - 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>;
> + };
> + };
> +
> + 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>;
> + };
> + opp-400000000 {
> + opp-hz = /bits/ 64 <400000000>;
> + /* 915 MB/s average and 3051 MB/s peak bandwidth */
> + opp-bw-MBs = <915 3051>;
> + };
> + opp-800000000 {
> + opp-hz = /bits/ 64 <800000000>;
> + /* 1830 MB/s average and 6103 MB/s peak bandwidth */
> + opp-bw-MBs = <1830 6103>;
> + };
> + opp-998400000 {
> + opp-hz = /bits/ 64 <998400000>;
> + /* 2282 MB/s average and 7614 MB/s peak bandwidth */
> + opp-bw-MBs = <2284 7614>;
> + };
> + };