Messages in this thread | | | Subject | Re: [PATCH 0/4] Introduce OPP bandwidth bindings | From | Sibi Sankar <> | Date | Sat, 16 Mar 2019 00:32:49 +0530 |
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On 3/13/19 2:30 PM, Georgi Djakov wrote: > Here is a proposal to extend the OPP bindings with bandwidth based on > a previous discussion [1]. > > Every functional block on a SoC can contribute to the system power > efficiency by expressing its own bandwidth needs (to memory or other SoC > modules). This will allow the system to save power when high throughput > is not required (and also provide maximum throughput when needed). > > There are at least three ways for a device to determine its bandwidth > needs: > 1. The device can dynamically calculate the needed bandwidth > based on some known variable. For example: UART (baud rate), I2C (fast > mode, high-speed mode, etc), USB (specification version, data transfer > type), SDHC (SD standard, clock rate, bus-width), Video Encoder/Decoder > (video format, resolution, frame-rate) > > 2. There is a hardware specific value. For example: hardware > specific constant value (e.g. for PRNG) or use-case specific value that > is hard-coded. > > 3. Predefined SoC/board specific bandwidth values. For example: > CPU or GPU bandwidth is related to the current core frequency and both > bandwidth and frequency are scaled together. > > This patchset is trying to address point 3 above by extending the OPP > bindings to support predefined SoC/board bandwidth values and adds > support in cpufreq-dt to scale the interconnect between the CPU and the > DDR together with frequency and voltage.
Hey Georgi, Having opp-bw-MBps as a part of cpu opp does greatly simplify the problem of scaling multiple interconnect devices with change in cpu frequency. But there is still a need to scale other devices (non interconnect based) according to cpu frequency. Having a devfreq governor for the same would help to have the same generic solution across SoCs (msm8916/8996/qcs405/sdm845). The devfreq maintainer did like the idea but wanted it incorporated into the passive governor.
* https://lore.kernel.org/lkml/20180528060014epcms1p87ec68a4d44f9447b06f979a87e545b7d@epcms1p8/
* https://lore.kernel.org/lkml/20180802095608epcms1p33fb061543efc9ceb3ec12d5567ceffbc@epcms1p3/
I have a RFC series implementing ddr scaling with passive governor for sdm845 with the following bindings, will post it early next week.
cpus { ...
CPU0: cpu@0 { ... operating-points-v2 = <&cpu0_opp_table>; ... }; ....
CPU4: cpu@400 { ... operating-points-v2 = <&cpu4_opp_table>; ... }; ... };
cpu0_opp_table: cpu0_opp_table { compatible = "operating-points-v2"; opp-shared;
cpu0_opp1: opp-300000000 { opp-hz = /bits/ 64 <300000000>; };
...
cpu0_opp16: opp-1612800000 { opp-hz = /bits/ 64 <1612800000>; };
... };
cpu4_opp_table: cpu4_opp_table { compatible = "operating-points-v2"; opp-shared;
...
cpu4_opp4: opp-1056000000 { opp-hz = /bits/ 64 <1056000000>; };
cpu4_opp5: opp-1209600000 { opp-hz = /bits/ 64 <1209600000>; };
... };
bw_opp_table: bw-opp-table { compatible = "operating-points-v2";
opp-200 { opp-hz = /bits/ 64 < 200000000 >; /* 200 MHz */ required-opps = <&cpu0_opp1>; /* 0 MB/s average and 762 MB/s peak bandwidth */ opp-bw-MBs = <0 762>; };
opp-300 { opp-hz = /bits/ 64 < 300000000 >; /* 300 MHz */ /* 0 MB/s average and 1144 MB/s peak bandwidth */ opp-bw-MBs = <0 1144>; };
...
opp-768 { opp-hz = /bits/ 64 < 768000000 >; /* 768 MHz */ /* 0 MB/s average and 2929 MB/s peak bandwidth */ opp-bw-MBs = <0 2929>; required-opps = <&cpu4_opp4>; };
opp-1017 { opp-hz = /bits/ 64 < 1017000000 >; /* 1017 MHz */ /* 0 MB/s average and 3879 MB/s peak bandwidth */ opp-bw-MBs = <0 3879>; required-opps = <&cpu0_opp16>, <&cpu4_opp5>; }; };
cpubw { compatible = "devfreq-icbw"; interconnects = <&snoc MASTER_APSS_1 &bimc SLAVE_EBI_CH0>; operating-points-v2 = <&bw_opp_table>; };
> > [1] https://patchwork.kernel.org/patch/10577315/ > > Georgi Djakov (4): > dt-bindings: opp: Introduce opp-bw-MBs bindings > OPP: Add support for parsing the interconnect bandwidth > OPP: Update the bandwidth on OPP frequency changes > cpufreq: dt: Add support for interconnect bandwidth scaling > > Documentation/devicetree/bindings/opp/opp.txt | 45 ++++++++++++ > drivers/cpufreq/cpufreq-dt.c | 27 ++++++- > drivers/opp/core.c | 71 +++++++++++++++++++ > drivers/opp/of.c | 44 ++++++++++++ > drivers/opp/opp.h | 6 ++ > include/linux/pm_opp.h | 14 ++++ > 6 files changed, 206 insertions(+), 1 deletion(-) >
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