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Message-ID: <20190608054711.GZ22737@tuxbook-pro>
Date: Fri, 7 Jun 2019 22:47:11 -0700
From: Bjorn Andersson <bjorn.andersson@...aro.org>
To: Saravana Kannan <saravanak@...gle.com>
Cc: Georgi Djakov <georgi.djakov@...aro.org>,
Rob Herring <robh+dt@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
Stephen Boyd <sboyd@...nel.org>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
Rajendra Nayak <rnayak@...eaurora.org>,
Jordan Crouse <jcrouse@...eaurora.org>,
vincent.guittot@...aro.org, amit.kucheria@...aro.org,
seansw@....qualcomm.com, daidavid1@...eaurora.org,
evgreen@...omium.org, sibis@...eaurora.org,
kernel-team@...roid.com, linux-pm@...r.kernel.org,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 0/9] Introduce Bandwidth OPPs & interconnect devfreq
driver
On Fri 07 Jun 21:43 PDT 2019, Saravana Kannan wrote:
> I replied[1] to this patch series[2] and described how I think interconnect
> bandwidth voting should be captured in DT and how it should work.
>
> So sending out a patch series implementing that. This patch series does the
> following:
> - Adds Bandwidth OPP table support (this adds device freq to bandwidth
> mapping for free)
> - Adds a devfreq library for interconnect paths
>
Please provide a driver that uses this devfreq library, without it this
its impossible to gauge the usefulness of your approach.
> Interconnects and interconnect paths quantify they performance levels in
> terms of bandwidth. So similar to how we have frequency based OPP tables
> in DT and in the OPP framework, this patch series adds bandwidth OPP
> table support in the OPP framework and in DT.
>
> To simplify voting for interconnects, this patch series adds helper
> functions to create devfreq devices out of interconnect paths. This
> allows drivers to add a single line of code to add interconnect voting
> capability.
>
> To add devfreq device for the "gpu-mem" interconnect path:
> icc_create_devfreq(dev, "gpu-mem");
>
> With the future addition of a "passive_bandwidth" devfreq governor,
> device frequency to interconnect bandwidth mapping would come for free.
>
> If the feedback on this patch series is positive, I'll then add the
> devfreq passive_bandwidth governor (or something similar) to v2 of this
> patch series.
>
> So with the DT bindings added in this patch series, the DT for a GPU
> that does bandwidth voting from GPU to Cache and GPU to DDR would look
> something like this:
>
> gpu_cache_opp_table: gpu_cache_opp_table {
> compatible = "operating-points-v2";
>
> gpu_cache_3000: opp-3000 {
> opp-peak-KBps = <3000>;
> opp-avg-KBps = <1000>;
> };
> gpu_cache_6000: opp-6000 {
> opp-peak-KBps = <6000>;
> opp-avg-KBps = <2000>;
> };
> gpu_cache_9000: opp-9000 {
> opp-peak-KBps = <9000>;
> opp-avg-KBps = <9000>;
> };
> };
>
> gpu_ddr_opp_table: gpu_ddr_opp_table {
> compatible = "operating-points-v2";
>
> gpu_ddr_1525: opp-1525 {
> opp-peak-KBps = <1525>;
> opp-avg-KBps = <452>;
> };
> gpu_ddr_3051: opp-3051 {
> opp-peak-KBps = <3051>;
> opp-avg-KBps = <915>;
> };
> gpu_ddr_7500: opp-7500 {
> opp-peak-KBps = <7500>;
> opp-avg-KBps = <3000>;
> };
> };
>
> gpu_opp_table: gpu_opp_table {
> compatible = "operating-points-v2";
> opp-shared;
>
> opp-200000000 {
> opp-hz = /bits/ 64 <200000000>;
> required-opps = <&gpu_cache_3000>, <&gpu_ddr_1525>;
I still don't see the benefit of the indirection, over just spelling out
the bandwidth values here.
Regards,
Bjorn
> };
> opp-400000000 {
> opp-hz = /bits/ 64 <400000000>;
> required-opps = <&gpu_cache_6000>, <&gpu_ddr_3051>;
> };
> };
>
> gpu@...4000 {
> ...
> operating-points-v2 = <&gpu_opp_table>, <&gpu_cache_opp_table>, <&gpu_ddr_opp_table>;
> interconnects = <&mmnoc MASTER_GPU_1 &bimc SLAVE_SYSTEL_CACHE>,
> <&mmnoc MASTER_GPU_1 &bimc SLAVE_DDR>;
> interconnect-names = "gpu-cache", "gpu-mem";
> interconnect-opp-table = <&gpu_cache_opp_table>, <&gpu_ddr_opp_table>
> };
>
> Cheers,
> Saravana
>
> [1] - https://lore.kernel.org/lkml/20190601021228.210574-1-saravanak@google.com/
> [2] - https://lore.kernel.org/lkml/20190423132823.7915-1-georgi.djakov@linaro.org/
>
> Saravana Kannan (9):
> dt-bindings: opp: Introduce opp-peak-KBps and opp-avg-KBps bindings
> OPP: Add support for bandwidth OPP tables
> OPP: Add helper function for bandwidth OPP tables
> OPP: Add API to find an OPP table from its DT node
> dt-bindings: interconnect: Add interconnect-opp-table property
> interconnect: Add OPP table support for interconnects
> OPP: Add function to look up required OPP's for a given OPP
> OPP: Allow copying OPPs tables between devices
> interconnect: Add devfreq support
>
> .../bindings/interconnect/interconnect.txt | 8 +
> Documentation/devicetree/bindings/opp/opp.txt | 15 +-
> drivers/interconnect/Makefile | 2 +-
> drivers/interconnect/core.c | 27 +++-
> drivers/interconnect/icc-devfreq.c | 144 ++++++++++++++++++
> drivers/opp/core.c | 109 +++++++++++++
> drivers/opp/of.c | 75 +++++++--
> drivers/opp/opp.h | 4 +-
> include/linux/interconnect.h | 17 +++
> include/linux/pm_opp.h | 41 +++++
> 10 files changed, 426 insertions(+), 16 deletions(-)
> create mode 100644 drivers/interconnect/icc-devfreq.c
>
> --
> 2.22.0.rc2.383.gf4fbbf30c2-goog
>
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