All of lore.kernel.org
 help / color / mirror / Atom feed
From: Hsin-Yi Wang <hsinyi@chromium.org>
To: Viresh Kumar <vireshk@kernel.org>, linux-pm@vger.kernel.org
Cc: Nishanth Menon <nm@ti.com>, Stephen Boyd <sboyd@kernel.org>,
	"Rafael J . Wysocki" <rjw@rjwysocki.net>,
	linux-kernel@vger.kernel.org,
	"MyungJoo Ham )" <myungjoo.ham@samsung.com>,
	Kyungmin Park <kyungmin.park@samsung.com>,
	Chanwoo Choi <cw00.choi@samsung.com>,
	Saravana Kannan <saravanak@google.com>
Subject: [PATCH v5 0/3] Add required-opps support to devfreq passive gov
Date: Wed,  3 Feb 2021 17:23:57 +0800	[thread overview]
Message-ID: <20210203092400.1791884-1-hsinyi@chromium.org> (raw)

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(-)

-- 
2.30.0.365.g02bc693789-goog


             reply	other threads:[~2021-02-03  9:27 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20210203092602epcas1p1550c96a2ed1b0b6d0a0f9f750cb76e45@epcas1p1.samsung.com>
2021-02-03  9:23 ` Hsin-Yi Wang [this message]
2021-02-03  9:23   ` [PATCH v5 1/3] OPP: Add function to look up required OPP's for a given OPP Hsin-Yi Wang
2021-02-04  5:46     ` Viresh Kumar
2021-02-03  9:23   ` [PATCH v5 2/3] PM / devfreq: Cache OPP table reference in devfreq Hsin-Yi Wang
2021-02-03  9:24   ` [PATCH v5 3/3] PM / devfreq: Add required OPPs support to passive governor Hsin-Yi Wang
2021-02-04  2:49     ` Viresh Kumar
2021-02-04  7:07       ` Hsin-Yi Wang
2021-02-03 10:12   ` [PATCH v5 0/3] Add required-opps support to devfreq passive gov Chanwoo Choi
2021-02-04  5:41   ` Viresh Kumar
2021-02-04  8:12     ` Hsin-Yi Wang
2021-02-04  8:53     ` Chanwoo Choi

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210203092400.1791884-1-hsinyi@chromium.org \
    --to=hsinyi@chromium.org \
    --cc=cw00.choi@samsung.com \
    --cc=kyungmin.park@samsung.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pm@vger.kernel.org \
    --cc=myungjoo.ham@samsung.com \
    --cc=nm@ti.com \
    --cc=rjw@rjwysocki.net \
    --cc=saravanak@google.com \
    --cc=sboyd@kernel.org \
    --cc=vireshk@kernel.org \
    --subject='Re: [PATCH v5 0/3] Add required-opps support to devfreq passive gov' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.