linux-kernel - Re: [PATCH v4 0/5] Add required-opps support to devfreq passive gov

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Date:   Thu, 14 Nov 2019 16:54:21 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Saravana Kannan <saravanak@...gle.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Sibi Sankar <sibis@...eaurora.org>, kernel-team@...roid.com,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/5] Add required-opps support to devfreq passive gov

Dear Saravana,

Any other progress of this series?

Regards,
Chanwoo Choi

On 7/24/19 10:42 AM, Saravana Kannan wrote:
> The devfreq passive governor scales the frequency of a "child" device based
> on the current frequency of a "parent" device (not parent/child in the
> sense of device hierarchy). As of today, the passive governor requires one
> of the following to work correctly:
> 1. The parent and child device have the same number of frequencies
> 2. The child device driver passes a mapping function to translate from
>    parent frequency to child frequency.
> 
> When (1) is not true, (2) is the only option right now. But often times,
> all that is required is a simple mapping from parent's frequency to child's
> frequency.
> 
> Since OPPs already support pointing to other "required-opps", add support
> for using that to map from parent device frequency to child device
> frequency. That way, every child device driver doesn't have to implement a
> separate mapping function anytime (1) isn't true.
> 
> Some common (but not comprehensive) reason for needing a devfreq passive
> governor to adjust the frequency of one device based on another are:
> 
> 1. These were the combination of frequencies that were validated/screened
>    during the manufacturing process.
> 2. These are the sensible performance combinations between two devices
>    interacting with each other. So that when one runs fast the other
>    doesn't become the bottleneck.
> 3. Hardware bugs requiring some kind of frequency ratio between devices.
> 
> For example, the following mapping can't be captured in DT as it stands
> today because the parent and child device have different number of OPPs.
> But with this patch series, this mapping can be captured cleanly.
> 
> In arch/arm64/boot/dts/exynos/exynos5433-bus.dtsi you have something
> like this with the following changes:
> 
> 	bus_g2d_400: bus0 {
> 		compatible = "samsung,exynos-bus";
> 		clocks = <&cmu_top CLK_ACLK_G2D_400>;
> 		clock-names = "bus";
> 		operating-points-v2 = <&bus_g2d_400_opp_table>;
> 		status = "disabled";
> 	};
> 
> 	bus_noc2: bus9 {
> 		compatible = "samsung,exynos-bus";
> 		clocks = <&cmu_mif CLK_ACLK_BUS2_400>;
> 		clock-names = "bus";
> 		operating-points-v2 = <&bus_noc2_opp_table>;
> 		status = "disabled";
> 	};
> 
> 	bus_g2d_400_opp_table: opp_table2 {
> 		compatible = "operating-points-v2";
> 		opp-shared;
> 
> 		opp-400000000 {
> 			opp-hz = /bits/ 64 <400000000>;
> 			opp-microvolt = <1075000>;
> 			required-opps = <&noc2_400>;
> 		};
> 		opp-267000000 {
> 			opp-hz = /bits/ 64 <267000000>;
> 			opp-microvolt = <1000000>;
> 			required-opps = <&noc2_200>;
> 		};
> 		opp-200000000 {
> 			opp-hz = /bits/ 64 <200000000>;
> 			opp-microvolt = <975000>;
> 			required-opps = <&noc2_200>;
> 		};
> 		opp-160000000 {
> 			opp-hz = /bits/ 64 <160000000>;
> 			opp-microvolt = <962500>;
> 			required-opps = <&noc2_134>;
> 		};
> 		opp-134000000 {
> 			opp-hz = /bits/ 64 <134000000>;
> 			opp-microvolt = <950000>;
> 			required-opps = <&noc2_134>;
> 		};
> 		opp-100000000 {
> 			opp-hz = /bits/ 64 <100000000>;
> 			opp-microvolt = <937500>;
> 			required-opps = <&noc2_100>;
> 		};
> 	};
> 
> 	bus_noc2_opp_table: opp_table6 {
> 		compatible = "operating-points-v2";
> 
> 		noc2_400: opp-400000000 {
> 			opp-hz = /bits/ 64 <400000000>;
> 		};
> 		noc2_200: opp-200000000 {
> 			opp-hz = /bits/ 64 <200000000>;
> 		};
> 		noc2_134: opp-134000000 {
> 			opp-hz = /bits/ 64 <134000000>;
> 		};
> 		noc2_100: opp-100000000 {
> 			opp-hz = /bits/ 64 <100000000>;
> 		};
> 	};
> 
> -Saravana
> 
> v3 -> v4:
> - Fixed documentation comments
> - Fixed order of functions in .h file
> - Renamed the new xlate API
> - Caused _set_required_opps() to fail if all required opps tables aren't
>   linked.
> v2 -> v3:
> - Rebased onto linux-next.
> - Added documentation comment for new fields.
> - Added support for lazy required-opps linking.
> - Updated Ack/Reviewed-bys.
> v1 -> v2:
> - Cached OPP table reference in devfreq to avoid looking up every time.
> - Renamed variable in passive governor to be more intuitive.
> - Updated cover letter with examples.
> 
> 
> Saravana Kannan (5):
>   OPP: Allow required-opps even if the device doesn't have power-domains
>   OPP: Add function to look up required OPP's for a given OPP
>   OPP: Improve required-opps linking
>   PM / devfreq: Cache OPP table reference in devfreq
>   PM / devfreq: Add required OPPs support to passive governor
> 
>  drivers/devfreq/devfreq.c          |   6 ++
>  drivers/devfreq/governor_passive.c |  20 ++++--
>  drivers/opp/core.c                 |  83 +++++++++++++++++++---
>  drivers/opp/of.c                   | 108 ++++++++++++++---------------
>  drivers/opp/opp.h                  |   5 ++
>  include/linux/devfreq.h            |   2 +
>  include/linux/pm_opp.h             |  11 +++
>  7 files changed, 165 insertions(+), 70 deletions(-)
>