linux-kernel - Re: [RFC v3 00/10] DDR/L3 Scaling support on SDM845 and SC7180 SoCs

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Date:   Wed, 29 Jan 2020 20:07:51 +0530
From:   Sibi Sankar <sibis@...eaurora.org>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     viresh.kumar@...aro.org, sboyd@...nel.org,
        georgi.djakov@...aro.org, saravanak@...gle.com, nm@...com,
        bjorn.andersson@...aro.org, agross@...nel.org,
        david.brown@...aro.org, robh+dt@...nel.org, mark.rutland@....com,
        rjw@...ysocki.net, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, dianders@...omium.org, mka@...omium.org,
        vincent.guittot@...aro.org, amit.kucheria@...aro.org,
        ulf.hansson@...aro.org, linux-arm-msm-owner@...r.kernel.org
Subject: Re: [RFC v3 00/10] DDR/L3 Scaling support on SDM845 and SC7180 SoCs

Hey Lukasz,
Thanks for taking time to review
the series!

On 2020-01-29 15:16, Lukasz Luba wrote:
> Hi Sibi,
> 
> In my opinion this solution depends on not always true assumption that
> CPUFreq notification chain will be triggered when there is a frequency

This series does not create any
devfreq devices nor use the cpufreq
notification chain. It just relies
on the opening up of required-opps
from being exclusive to gen-pd using
patches 1,2,3 from patch series[1].
With the fast path disabled and
schedutil enabled, this series will
not miss any cpufreq changes.

[1] https://patchwork.kernel.org/cover/11055499/

> switch. Extending devfreq governor (as in one of the dependent patch
> series that you have referred) by attaching to this notification
> chain makes sense only when the SchedUtil and fast_switch is not in 
> use.

fast_switch and cpu notifier chains
are mutually exclusive but schedutil
will still operate in the slow path
IIRC.

> The Schedutil CPUFreq governor might use the fast_switch from this
> driver and the notifications will not be triggered. I have also
> commented patch 08/10 which tries to disable it.
> 
> Regards,
> Lukasz
> 
> On 1/27/20 8:03 PM, Sibi Sankar wrote:
>> This RFC series aims to extend cpu based scaling support to L3/DDR on
>> SDM845 and SC7180 SoCs.
>> 
>> Patches [1-3] - Blacklist SDM845 and SC7180 in cpufreq-dt-platdev
>> Patches [5-7] - Hack in a way to add/remove multiple opp tables to
>>                  a single device. I am yet to fix the debugfs to
>> 		support multiple opp_tables per device but wanted to
>> 		send what was working upstream to get an idea if multiple
>> 		opp tables per device is a feature that will be useful
>> 		upstream.
>> Patches [9-10] - Add the cpu/cpu-ddr/cpu-l3 opp tables for SDM845
>>                   and SC7180 SoCs.
>> 
>> v3:
>>   * Migrated to using Saravana's opp-kBps bindings [1]
>>   * Fixed some misc comments from Rajendra
>>   * Added support for SC7180
>> 
>> v2:
>>   * Incorporated Viresh's comments from:
>>   
>> https://lore.kernel.org/lkml/20190410102429.r6j6brm5kspmqxc3@vireshk-i7/
>>   
>> https://lore.kernel.org/lkml/20190410112516.gnh77jcwawvld6et@vireshk-i7/
>>   * Dropped cpufreq-map passive governor
>> 
>> Git-branch: https://github.com/QuinAsura/linux/tree/lnext-012420
>> 
>> Some alternate ways of hosting the opp-tables:
>> https://github.com/QuinAsura/linux/commit/50b92bfaadc8f9a0d1e12249646e018bd6d1a9d3
>> https://github.com/QuinAsura/linux/commit/3d23d1eefd16ae6d9e3ef91e93e78749d8844e98
>> Viresh didn't really like ^^ bindings and they dont really scale well. 
>> Just
>> including them here for completeness.
>> 
>> Depends on the following series:
>> [1] https://patchwork.kernel.org/cover/11277199/
>> [2] https://patchwork.kernel.org/cover/11055499/
>> [3] https://patchwork.kernel.org/cover/11326381/
>> 
>> Sibi Sankar (10):
>>    arm64: dts: qcom: sdm845: Add SoC compatible to MTP
>>    cpufreq: blacklist SDM845 in cpufreq-dt-platdev
>>    cpufreq: blacklist SC7180 in cpufreq-dt-platdev
>>    OPP: Add and export helper to update voltage
>>    opp: of: export _opp_of_get_opp_desc_node
>>    opp: Allow multiple opp_tables to be mapped to a single device
>>    opp: Remove multiple attached opp tables from a device
>>    cpufreq: qcom: Update the bandwidth levels on frequency change
>>    arm64: dts: qcom: sdm845: Add cpu OPP tables
>>    arm64: dts: qcom: sc7180: Add cpu OPP tables
>> 
>>   arch/arm64/boot/dts/qcom/sc7180.dtsi    | 287 +++++++++++++++
>>   arch/arm64/boot/dts/qcom/sdm845-mtp.dts |   2 +-
>>   arch/arm64/boot/dts/qcom/sdm845.dtsi    | 453 
>> ++++++++++++++++++++++++
>>   drivers/cpufreq/cpufreq-dt-platdev.c    |   2 +
>>   drivers/cpufreq/qcom-cpufreq-hw.c       | 246 +++++++++++--
>>   drivers/opp/core.c                      | 111 +++++-
>>   drivers/opp/of.c                        |   3 +-
>>   drivers/opp/opp.h                       |   2 +
>>   include/linux/pm_opp.h                  |  10 +
>>   9 files changed, 1083 insertions(+), 33 deletions(-)
>> 

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