Re: [PATCH v5 0/3] Add required-opps support to devfreq passive gov

[Chanwoo Choi <cw00.choi@samsung.com>]

Hi Hsin-Yi,

Thanks for the patch. I already reviewed this patch.
But, I'll check these again and test it. 

On 2/3/21 6:23 PM, Hsin-Yi Wang 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
> 
> v4 -> v5:
> - drop patch "OPP: Improve required-opps linking" and rebase to 
>   https://git.kernel.org/pub/scm/linux/kernel/git/vireshk/pm.git/log/?h=opp/linux-next
> - Compare pointers in dev_pm_opp_xlate_required_opp().
> 
> 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 (3):
>   OPP: Add function to look up required OPP's for a given OPP
>   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                 | 58 ++++++++++++++++++++++++++++++
>  include/linux/devfreq.h            |  2 ++
>  include/linux/pm_opp.h             | 11 ++++++
>  5 files changed, 92 insertions(+), 5 deletions(-)
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics