Re: [PATCH v7 05/20] PM / devfreq: Add new passive governor

Re: [PATCH v7 05/20] PM / devfreq: Add new passive governor

[MyungJoo Ham]

>   
>  This patch adds the new passive governor for DEVFREQ framework. The following
> governors are already present and used for DVFS (Dynamic Voltage and Frequency
> Scaling) drivers. The following governors are independently used for one device
[]
> Suggested-by: Myungjoo Ham <myungjoo.ham@samsung.com>
> Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
> [tjakobi: Reported RCU locking issue and cw00.choi fix it.]
> Reported-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>

Please just edit the comment below and push to your git repo so that
I can simply pull your repo a day or two later.

> ---
>  drivers/devfreq/Kconfig            |   8 ++
>  drivers/devfreq/Makefile           |   1 +
>  drivers/devfreq/governor_passive.c | 206 +++++++++++++++++++++++++++++++++++++
>  include/linux/devfreq.h            |  33 ++++++
>  4 files changed, 248 insertions(+)
>  create mode 100644 drivers/devfreq/governor_passive.c
> 
> diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
> index cedda8f1e5eb..d260cd0219f6 100644
[]
> diff --git a/drivers/devfreq/Makefile b/drivers/devfreq/Makefile
> index 8af8aaf922a8..2633087d5c63 100644
[]
> diff --git a/drivers/devfreq/governor_passive.c b/drivers/devfreq/governor_passive.c
> +	/*
> +	 * If the parent and passive devfreq device uses the OPP table,
> +	 * get the next frequency by using the OPP table.

Doesn't need comments from here
> +	 * - parent devfreq device uses the governors except for passive.
> +	 * - passive devfreq device uses the passive governor.
> +	 */
> +
> +	/*
To here.

> +	 * Each devfreq has the OPP table. After deciding the new frequency
> +	 * from the governor of parent devfreq device, the passive governor
> +	 * need to get the index of new frequency on OPP table of parent
> +	 * device. And then the index is used for getting the suitable
> +	 * new frequency for passive devfreq device.
> +	 */

[]

> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
> index 98c699304e12..2de4e2eea180 100644
[]

[PATCH v7 00/20] PM / devferq: Add generic exynos bus frequency driver and new passive governor

[Chanwoo Choi]

This patch-set includes the two features as following. The generic exynos bus
frequency driver is able to support almost Exynos SoCs for bus frequency
scaling. And the new passive governor is able to make the dependency on
between devices for frequency/voltage scaling. I had posted the patch-set[1]
with the similiar concept. This is is revised version for exynos bus frequency.
- Generic exynos bus frequency driver
- New passive governor of DEVFREQ framework
[1] https://lkml.org/lkml/2015/1/7/872
: [PATCHv3 0/8] devfreq: Add generic exynos memory-bus frequency driver


Changes from v6:
(https://lkml.org/lkml/2016/3/27/187)
- Patch1/2 add signed-off-by tag from DEVFREQ Maintainer (Myungjoo Ham)
- Drop patch5 (PM / devfreq: Add governer type with unique number)
- Add missing description about the transition_notifier_list in struct devfreq
- Remove the passive governor code from devfreq.c core driver. Instead, passive
  governor uses the DEVFREQ_GOV_START/STOP signal to register/unregister the
  DEVFREQ_TRANSITION_NOTIFIER between the parent devfreq device and passive
  devfreq device.
- Add the author (myungjoo.ham@samsung.com) of passive governor 
- Add 'struct devfreq_passive_data' to pass the devfreq instance of parent.

Changes from v5:
(https://lkml.org/lkml/2016/3/24/5)
- Rebase the patch-set on Linux v4.6-rc1
- Add Tested-by tag from Markus Reichl <m.reichl@fivetechno.de>
- Add Tested-by tag from Anand Moon <linux.amoon@gmail.com>

Changes from v4:
(https://lkml.org/lkml/2015/12/14/43)
- Add new DEVFREQ_TRANSITION_NOTIFIER notifier. The passive
  devfreq device recevie the changed frequency of parent
  devfreq device through DEVFREQ_TRANSITION_NOTIFIER.
- Add governor type to identify thme using the defined constant
- Modify the passive governor using the DEVFREQ_TRANSITION_NOTIFIER notifier.
- Fix the RCU locking probrlm (Reported-by: Tobias Jakobi)
- Fix the debugfs error during the kernel booting (Reported-by: Tobias Jakobi)
- The Device Tree patches have got Reviewed-by tag from Exynos SoC Maintainer
  (Krzysztof Kozlowski <k.kozlowski@samsung.com>)

Changes from v3:
(https://lkml.org/lkml/2015/12/11/75)
- Add the reviewed-by tag from Krzysztof Kozlowski (patch2/3/13/14/15/16/17)
- Fix typo of the description on patch14
- Modify the subject and description of patch17
- Reorder the 'bus_xxx' device tree node alphabetically in 
  both exynos3250-rinato/monk.dts and exynos4412-trats/odroidu3

Changes from v2:
(https://lkml.org/lkml/2015/12/8/869)
- Fix typo on documentation
- Modify the more appropriate sentence on patch description
- Add the detailed description about both parent and passive bus device
- Modify the DMC frequency for Exynos4x12 DMC bus (200MHz -> 267MHz)
- Modify the voltage of 200MHz was included in Exynos3250 DMC bus (800mV -> 825mV)
- Rename OPP nodes as 'opp@<opp-hz>'
- Delete the duplicate 'opp-microvolt' property of passive devfreq device
- Reorder the 'bus_xxx' device tree node alphabetically in exynos3250-rinato/monk.dts
- Reorder the 'bus_xxx' device tree node alphabetically in exynos4412-trats/odroidu3
- Add new exynos4412-ppmu-common.dtsi to remove the duplicate PPMU dt node
  on rinato/monk/trats2/odroid-u3 board
- Add the log message if bus device is registered to devfreq framework successfully
- Add the reviewed-by tag from Krzysztof Kozlowski
- Add the tested-by tag from Anand Moon on Odroid U3
- Add 'SAMSUNG BUS FREQUENCY DRIVER' entry to MAINTAINERS

Changes from v1:
(https://lkml.org/lkml/2015/11/26/260)
- Check whether the instance of regulator is NULL or not
  when executing regulator_disable() because of only parent
  devfreq device has the regulator instance. After fixing it,
  the wake-up from suspend state is well working. (patch1)
- Fix bug which checks 'bus-clk' instead of 'bus->regulator'
  after calling devm_clk_get() (on patch1)
- Update the documentation to remove the description about
  DEVFREQ-EVENT subsystem (on patch2)
- Add the full name of DMC (Dynamic Memory Controller) (on patch2)
- Modify the detailed correlation of buses for Exynos3250
  on documentation (patch2)
- Add the MFC bus node for Exynos3250 (on patch11, patch12)
- Fix the duplicate frequency of bus_display on Exynos4x12.dtsi
- Add the PPMU node for exynos4412-odroidu3
- Add the support of bus frequency for exynos4412-odroidu3


[Description]
Detailed descirption for patch-set:
1. Add generic exynos bus frequency driver
: This patch-set adds the generic exynos bus frequency driver for AXI bus
of sub-blocks in exynos SoC. The Samsung Exynos SoC have the common
architecture for bus between DRAM and sub-blocks in SoC.

 There are the different buses according to Exynos SoC because Exynos SoC
has the differnt sub-blocks and bus speed. In spite of this difference
among Exynos SoCs, this driver is able to support almost Exynos SoC by adding
unique data of each bus in the devicetree file.

 In devicetree, each bus node has a bus clock, regulator, operation-point
and devfreq-event devices which measure the utilization of each bus block.

For example,
- The bus of DMC block in exynos3250.dtsi are listed below:

	bus_dmc: bus_dmc {
		compatible = "samsung,exynos-bus";
		clocks = <&cmu_dmc CLK_DIV_DMC>;
		clock-names = "bus";
		operating-points-v2 = <&bus_dmc_opp_table>;
		status = "disabled";
	};

	bus_dmc_opp_table: opp_table1 {
		compatible = "operating-points-v2";
		opp-shared;

		opp@50000000 {
			opp-hz = /bits/ 64 <50000000>;
			opp-microvolt = <800000>;
		};
		opp@100000000 {
			opp-hz = /bits/ 64 <100000000>;
			opp-microvolt = <800000>;
		};
		opp@134000000 {
			opp-hz = /bits/ 64 <134000000>;
			opp-microvolt = <800000>;
		};
		opp@200000000 {
			opp-hz = /bits/ 64 <200000000>;
			opp-microvolt = <825000>;
		};
		opp@400000000 {
			opp-hz = /bits/ 64 <400000000>;
			opp-microvolt = <875000>;
		};
	};

- Usage case to handle the frequency and voltage of bus on runtime
  in exynos3250-rinato.dts are listed below:

	&bus_dmc {
		devfreq-events = <&ppmu_dmc0_3>, <&ppmu_dmc1_3>;
		vdd-supply = <&buck1_reg>;	/* VDD_MIF */
		status = "okay";
	};

2. Add new passive governor of DEVFREQ framework
: This patch-set add the new passive governor for DEVFREQ framework.
The existing governors (ondemand, performance and so on) are used for DVFS
(Dynamic Voltage and Frequency Scaling) drivers. The existing governors
are independently used for specific device driver which don't give the
influence to other device drviers and also don't receive the effect from
other device drivers.

 The passive governor depends on operation of parent driver with existing
governors(ondemand, performance and so on) extremely and is not able to
decide the new frequency by oneself. According to the decided new frequency
of parent driver with governor, the passive governor uses it to decide
the appropriate frequency for own device driver. The passive governor
must need the following information from device tree:

For exameple,
 There are one more bus device drivers in Exynos3250 which need to
change their source clock according to their utilization on runtime.
But, they share the same power line (e.g., regulator). So, LEFTBUS bus
driver is operated as parent with ondemand governor and then the rest
device driver with passive governor.

 The buses of Internal block in exynos3250.dtsi are listed below:
When LEFTBUS bus driver (parent) changes the bus frequency with
ondemand governor on runtime, the rest bus devices which sharing
the same power line (VDD_INT) will change the each bus frequency
according to the decision of LEFTBUS bus driver (parent).

- INT (Internal) block
	: VDD_INT |--- LEFTBUS
		  |--- PERIL
		  |--- MFC
		  |--- G3D
		  |--- RIGHTBUS
		  |--- FSYS
		  |--- LCD0
		  |--- PERIR
		  |--- ISP
		  |--- CAM

- The buss of INT block in exynos3250.dtsi are listed below:
	bus_leftbus: bus_leftbus {
		compatible = "samsung,exynos-bus";
		clocks = <&cmu CLK_DIV_GDL>;
		clock-names = "bus";
		operating-points-v2 = <&bus_leftbus_opp_table>;
		status = "disabled";
	};

	bus_rightbus: bus_rightbus {
		compatible = "samsung,exynos-bus";
		clocks = <&cmu CLK_DIV_GDR>;
		clock-names = "bus";
		operating-points-v2 = <&bus_leftbus_opp_table>;
		status = "disabled";
	};

	(Omit the rest bus dt node)

- Usage case to handle the frequency and voltage of bus on runtime
  in exynos3250-rinato.dts are listed below:
	/* Parent bus device of VDD_INT */
	&bus_leftbus {
		devfreq-events = <&ppmu_leftbus_3>, <&ppmu_rightbus_3>;
		vdd-supply = <&buck3_reg>;
		status = "okay";
	};

	/* Passive bus device depend on LEFTBUS bus. */
	&bus_rightbus {
		devfreq = <&bus_leftbus>; /* 'devfreq' property indicates
					     the phandle of parent device. */
		status = "okay";
	};

	(Omit the rest bus dt node)

Chanwoo Choi (20):
  PM / devfreq: exynos: Add generic exynos bus frequency driver
  PM / devfreq: exynos: Add documentation for generic exynos bus frequency driver
  PM / devfreq: Add devfreq_get_devfreq_by_phandle()
  PM / devfreq: Add new DEVFREQ_TRANSITION_NOTIFIER notifier
  PM / devfreq: Add new passive governor
  PM / devfreq: exynos: Add support of bus frequency of sub-blocks using passive governor
  PM / devfreq: exynos: Update documentation for bus devices using passive governor
  PM / devfreq: exynos: Add the detailed correlation between sub-blocks and power line
  PM / devfreq: exynos: Remove unused exynos4/5 busfreq driver
  MAINTAINERS: Add samsung bus frequency driver entry
  ARM: dts: Add DMC bus node for Exynos3250
  ARM: dts: Add DMC bus frequency for exynos3250-rinato/monk
  ARM: dts: Add bus nodes using VDD_INT for Exynos3250
  ARM: dts: Add bus nodes using VDD_MIF for Exynos4x12
  ARM: dts: Add bus nodes using VDD_INT for Exynos4x12
  ARM: dts: Add bus nodes using VDD_MIF for Exynos4210
  ARM: dts: Add exynos4412-ppmu-common dtsi to delete duplicate PPMU nodes
  ARM: dts: Add support of bus frequency using VDD_INT for exynos3250-rinato
  ARM: dts: Expand the voltage range of buck1/3 regulator for exynos4412-odroidu3
  ARM: dts: Add support of bus frequency for exynos4412-trats/odroidu3

 .../devicetree/bindings/devfreq/exynos-bus.txt     |  390 ++++++++
 MAINTAINERS                                        |    9 +
 arch/arm/boot/dts/exynos3250-monk.dts              |   47 +-
 arch/arm/boot/dts/exynos3250-rinato.dts            |   88 +-
 arch/arm/boot/dts/exynos3250.dtsi                  |  181 ++++
 arch/arm/boot/dts/exynos4210.dtsi                  |  159 +++
 arch/arm/boot/dts/exynos4412-odroid-common.dtsi    |   56 +-
 arch/arm/boot/dts/exynos4412-ppmu-common.dtsi      |   50 +
 arch/arm/boot/dts/exynos4412-trats2.dts            |   88 +-
 arch/arm/boot/dts/exynos4x12.dtsi                  |  174 ++++
 drivers/devfreq/Kconfig                            |   36 +-
 drivers/devfreq/Makefile                           |    4 +-
 drivers/devfreq/devfreq.c                          |  207 +++-
 drivers/devfreq/exynos-bus.c                       |  570 +++++++++++
 drivers/devfreq/exynos/Makefile                    |    3 -
 drivers/devfreq/exynos/exynos4_bus.c               | 1055 --------------------
 drivers/devfreq/exynos/exynos4_bus.h               |  110 --
 drivers/devfreq/exynos/exynos5_bus.c               |  431 --------
 drivers/devfreq/exynos/exynos_ppmu.c               |  119 ---
 drivers/devfreq/exynos/exynos_ppmu.h               |   86 --
 drivers/devfreq/governor_passive.c                 |  206 ++++
 include/linux/devfreq.h                            |   99 ++
 22 files changed, 2220 insertions(+), 1948 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/devfreq/exynos-bus.txt
 create mode 100644 arch/arm/boot/dts/exynos4412-ppmu-common.dtsi
 create mode 100644 drivers/devfreq/exynos-bus.c
 delete mode 100644 drivers/devfreq/exynos/Makefile
 delete mode 100644 drivers/devfreq/exynos/exynos4_bus.c
 delete mode 100644 drivers/devfreq/exynos/exynos4_bus.h
 delete mode 100644 drivers/devfreq/exynos/exynos5_bus.c
 delete mode 100644 drivers/devfreq/exynos/exynos_ppmu.c
 delete mode 100644 drivers/devfreq/exynos/exynos_ppmu.h
 create mode 100644 drivers/devfreq/governor_passive.c

-- 
1.9.1

[PATCH v7 05/20] PM / devfreq: Add new passive governor

[Chanwoo Choi]

This patch adds the new passive governor for DEVFREQ framework. The following
governors are already present and used for DVFS (Dynamic Voltage and Frequency
Scaling) drivers. The following governors are independently used for one device
driver which don't give the influence to other device drviers and also don't
receive the effect from other device drivers.
- ondemand / performance / powersave / userspace

The passive governor depends on operation of parent driver with specific
governos extremely and is not able to decide the new frequency by oneself.
According to the decided new frequency of parent driver with governor,
the passive governor uses it to decide the appropriate frequency for own
device driver. The passive governor must need the following information
from device tree:
- the source clock and OPP tables
- the instance of parent device

For exameple,
there are one more devfreq device drivers which need to change their source
clock according to their utilization on runtime. But, they share the same
power line (e.g., regulator). So, specific device driver is operated as parent
with ondemand governor and then the rest device driver with passive governor
is influenced by parent device.

Suggested-by: Myungjoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
[tjakobi: Reported RCU locking issue and cw00.choi fix it.]
Reported-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
---
 drivers/devfreq/Kconfig            |   8 ++
 drivers/devfreq/Makefile           |   1 +
 drivers/devfreq/governor_passive.c | 206 +++++++++++++++++++++++++++++++++++++
 include/linux/devfreq.h            |  33 ++++++
 4 files changed, 248 insertions(+)
 create mode 100644 drivers/devfreq/governor_passive.c

diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
index cedda8f1e5eb..d260cd0219f6 100644
--- a/drivers/devfreq/Kconfig
+++ b/drivers/devfreq/Kconfig
@@ -64,6 +64,14 @@ config DEVFREQ_GOV_USERSPACE
 	  Otherwise, the governor does not change the frequency
 	  given at the initialization.
 
+config DEVFREQ_GOV_PASSIVE
+	tristate "Passive"
+	help
+	  Sets the frequency based on the frequency of its parent devfreq
+	  device. This governor does not change the frequency by itself
+	  through sysfs entries. The passive governor recommends that
+	  devfreq device uses the OPP table to get the frequency/voltage.
+
 comment "DEVFREQ Drivers"
 
 config ARM_EXYNOS_BUS_DEVFREQ
diff --git a/drivers/devfreq/Makefile b/drivers/devfreq/Makefile
index 8af8aaf922a8..2633087d5c63 100644
--- a/drivers/devfreq/Makefile
+++ b/drivers/devfreq/Makefile
@@ -4,6 +4,7 @@ obj-$(CONFIG_DEVFREQ_GOV_SIMPLE_ONDEMAND)	+= governor_simpleondemand.o
 obj-$(CONFIG_DEVFREQ_GOV_PERFORMANCE)	+= governor_performance.o
 obj-$(CONFIG_DEVFREQ_GOV_POWERSAVE)	+= governor_powersave.o
 obj-$(CONFIG_DEVFREQ_GOV_USERSPACE)	+= governor_userspace.o
+obj-$(CONFIG_DEVFREQ_GOV_PASSIVE)	+= governor_passive.o
 
 # DEVFREQ Drivers
 obj-$(CONFIG_ARM_EXYNOS_BUS_DEVFREQ)	+= exynos-bus.o
diff --git a/drivers/devfreq/governor_passive.c b/drivers/devfreq/governor_passive.c
new file mode 100644
index 000000000000..4fd5c1fbf23d
--- /dev/null
+++ b/drivers/devfreq/governor_passive.c
@@ -0,0 +1,206 @@
+/*
+ * linux/drivers/devfreq/governor_passive.c
+ *
+ * Copyright (C) 2016 Samsung Electronics
+ * Author: Chanwoo Choi <cw00.choi@samsung.com>
+ * Author: MyungJoo Ham <myungjoo.ham@samsung.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/devfreq.h>
+#include "governor.h"
+
+static int devfreq_passive_get_target_freq(struct devfreq *devfreq,
+					unsigned long *freq)
+{
+	struct devfreq_passive_data *p_data
+			= (struct devfreq_passive_data *)devfreq->data;
+	struct devfreq *parent_devfreq = (struct devfreq *)p_data->parent;
+	unsigned long child_freq = ULONG_MAX;
+	struct dev_pm_opp *opp;
+	int i, count, ret = 0;
+
+	/*
+	 * If the devfreq device with passive governor has the specific method
+	 * to determine the next frequency, should use the get_target_freq()
+	 * of struct devfreq_passive_data.
+	 */
+	if (p_data->get_target_freq) {
+		ret = p_data->get_target_freq(devfreq, freq);
+		goto out;
+	}
+
+	/*
+	 * If the parent and passive devfreq device uses the OPP table,
+	 * get the next frequency by using the OPP table.
+	 * - parent devfreq device uses the governors except for passive.
+	 * - passive devfreq device uses the passive governor.
+	 */
+
+	/*
+	 * Each devfreq has the OPP table. After deciding the new frequency
+	 * from the governor of parent devfreq device, the passive governor
+	 * need to get the index of new frequency on OPP table of parent
+	 * device. And then the index is used for getting the suitable
+	 * new frequency for passive devfreq device.
+	 */
+	if (!devfreq->profile || !devfreq->profile->freq_table
+		|| devfreq->profile->max_state <= 0)
+		return -EINVAL;
+
+	/*
+	 * The passive governor have to get the correct frequency from OPP
+	 * list of parent device. Because in this case, *freq is temporary
+	 * value which is decided by ondemand governor.
+	 */
+	rcu_read_lock();
+	opp = devfreq_recommended_opp(parent_devfreq->dev.parent, freq, 0);
+	rcu_read_unlock();
+	if (IS_ERR_OR_NULL(opp)) {
+		ret = PTR_ERR(opp);
+		goto out;
+	}
+
+	/*
+	 * Get the OPP table's index of decided freqeuncy by governor
+	 * of parent device.
+	 */
+	for (i = 0; i < parent_devfreq->profile->max_state; i++)
+		if (parent_devfreq->profile->freq_table[i] == *freq)
+			break;
+
+	if (i == parent_devfreq->profile->max_state) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	/* Get the suitable frequency by using index of parent device. */
+	if (i < devfreq->profile->max_state) {
+		child_freq = devfreq->profile->freq_table[i];
+	} else {
+		count = devfreq->profile->max_state;
+		child_freq = devfreq->profile->freq_table[count - 1];
+	}
+
+	/* Return the suitable frequency for passive device. */
+	*freq = child_freq;
+
+out:
+	return ret;
+}
+
+static int update_devfreq_passive(struct devfreq *devfreq, unsigned long freq)
+{
+	int ret;
+
+	if (!devfreq->governor)
+		return -EINVAL;
+
+	mutex_lock(&devfreq->lock);
+
+	ret = devfreq->governor->get_target_freq(devfreq, &freq);
+	if (ret < 0)
+		goto out;
+
+	ret = devfreq->profile->target(devfreq->dev.parent, &freq, 0);
+	if (ret < 0)
+		goto out;
+
+	devfreq->previous_freq = freq;
+
+out:
+	mutex_unlock(&devfreq->lock);
+
+	return 0;
+}
+
+static int devfreq_passive_notifier_call(struct notifier_block *nb,
+				unsigned long event, void *ptr)
+{
+	struct devfreq_passive_data *data
+			= container_of(nb, struct devfreq_passive_data, nb);
+	struct devfreq *devfreq = (struct devfreq *)data->this;
+	struct devfreq *parent = (struct devfreq *)data->parent;
+	struct devfreq_freqs *freqs = (struct devfreq_freqs *)ptr;
+	unsigned long freq = freqs->new;
+
+	switch (event) {
+	case DEVFREQ_PRECHANGE:
+		if (parent->previous_freq > freq)
+			update_devfreq_passive(devfreq, freq);
+		break;
+	case DEVFREQ_POSTCHANGE:
+		if (parent->previous_freq < freq)
+			update_devfreq_passive(devfreq, freq);
+		break;
+	}
+
+	return NOTIFY_DONE;
+}
+
+static int devfreq_passive_event_handler(struct devfreq *devfreq,
+				unsigned int event, void *data)
+{
+	struct device *dev = devfreq->dev.parent;
+	struct devfreq_passive_data *p_data
+			= (struct devfreq_passive_data *)devfreq->data;
+	struct devfreq *parent = (struct devfreq *)p_data->parent;
+	struct notifier_block *nb = &p_data->nb;
+	int ret = 0;
+
+	if (!parent)
+		return -EPROBE_DEFER;
+
+	switch (event) {
+	case DEVFREQ_GOV_START:
+		if (!p_data->this)
+			p_data->this = devfreq;
+
+		nb->notifier_call = devfreq_passive_notifier_call;
+		ret = devm_devfreq_register_notifier(dev, parent, nb,
+					DEVFREQ_TRANSITION_NOTIFIER);
+		break;
+	case DEVFREQ_GOV_STOP:
+		devm_devfreq_unregister_notifier(dev, parent, nb,
+					DEVFREQ_TRANSITION_NOTIFIER);
+		break;
+	default:
+		break;
+	}
+
+	return ret;
+}
+
+static struct devfreq_governor devfreq_passive = {
+	.name = "passive",
+	.get_target_freq = devfreq_passive_get_target_freq,
+	.event_handler = devfreq_passive_event_handler,
+};
+
+static int __init devfreq_passive_init(void)
+{
+	return devfreq_add_governor(&devfreq_passive);
+}
+subsys_initcall(devfreq_passive_init);
+
+static void __exit devfreq_passive_exit(void)
+{
+	int ret;
+
+	ret = devfreq_remove_governor(&devfreq_passive);
+	if (ret)
+		pr_err("%s: failed remove governor %d\n", __func__, ret);
+
+	return;
+}
+module_exit(devfreq_passive_exit);
+
+MODULE_AUTHOR("Chanwoo Choi <cw00.choi@samsung.com>");
+MODULE_AUTHOR("MyungJoo Ham <myungjoo.ham@samsung.com>");
+MODULE_DESCRIPTION("DEVFREQ Passive governor");
+MODULE_LICENSE("GPL v2");
diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
index 98c699304e12..2de4e2eea180 100644
--- a/include/linux/devfreq.h
+++ b/include/linux/devfreq.h
@@ -272,6 +272,39 @@ struct devfreq_simple_ondemand_data {
 };
 #endif
 
+#if IS_ENABLED(CONFIG_DEVFREQ_GOV_PASSIVE)
+/**
+ * struct devfreq_passive_data - void *data fed to struct devfreq
+ *	and devfreq_add_device
+ * @parent:	the devfreq instance of parent device.
+ * @get_target_freq:	Optional callback, Returns desired operating frequency
+ *			for the device using passive governor. That is called
+ *			when passive governor should decide the next frequency
+ *			by using the new frequency of parent devfreq device
+ *			using governors except for passive governor.
+ *			If the devfreq device has the specific method to decide
+ *			the next frequency, should use this callback.
+ * @this:	the devfreq instance of own device.
+ * @nb:		the notifier block for DEVFREQ_TRANSITION_NOTIFIER list
+ *
+ * The devfreq_passive_data have to set the devfreq instance of parent
+ * device with governors except for the passive governor. But, don't need to
+ * initialize the 'this' and 'nb' field because the devfreq core will handle
+ * them.
+ */
+struct devfreq_passive_data {
+	/* Should set the devfreq instance of parent device */
+	struct devfreq *parent;
+
+	/* Optional callback to decide the next frequency of passvice device */
+	int (*get_target_freq)(struct devfreq *this, unsigned long *freq);
+
+	/* For passive governor's internal use. Don't need to set them */
+	struct devfreq *this;
+	struct notifier_block nb;
+};
+#endif
+
 #else /* !CONFIG_PM_DEVFREQ */
 static inline struct devfreq *devfreq_add_device(struct device *dev,
 					  struct devfreq_dev_profile *profile,
-- 
1.9.1