Re: [v5, PATCH 4/5] cpufreq: mediatek: add opp notification for SVS support

Re: [v5, PATCH 4/5] cpufreq: mediatek: add opp notification for SVS support

[Viresh Kumar]

On 26-11-19, 19:50, Andrew-sh.Cheng wrote:
> diff --git a/drivers/cpufreq/mediatek-cpufreq.c b/drivers/cpufreq/mediatek-cpufreq.c
> index 4b0cc50dd93b..7c37ab31230a 100644
> --- a/drivers/cpufreq/mediatek-cpufreq.c
> +++ b/drivers/cpufreq/mediatek-cpufreq.c
> @@ -42,6 +42,10 @@ struct mtk_cpu_dvfs_info {
>  	struct list_head list_head;
>  	int intermediate_voltage;
>  	bool need_voltage_tracking;
> +	struct mutex lock; /* avoid notify and policy race condition */

Will a read-write lock be better suited here for performance reasons ?

> +	struct notifier_block opp_nb;
> +	int opp_cpu;
> +	unsigned long opp_freq;
>  };
>  
>  static LIST_HEAD(dvfs_info_list);
> @@ -231,6 +235,7 @@ static int mtk_cpufreq_set_target(struct cpufreq_policy *policy,
>  	vproc = dev_pm_opp_get_voltage(opp);
>  	dev_pm_opp_put(opp);
>  
> +	mutex_lock(&info->lock);
>  	/*
>  	 * If the new voltage or the intermediate voltage is higher than the
>  	 * current voltage, scale up voltage first.
> @@ -242,6 +247,7 @@ static int mtk_cpufreq_set_target(struct cpufreq_policy *policy,
>  			pr_err("cpu%d: failed to scale up voltage!\n",
>  			       policy->cpu);
>  			mtk_cpufreq_set_voltage(info, old_vproc);
> +			mutex_unlock(&info->lock);
>  			return ret;
>  		}
>  	}
> @@ -253,6 +259,7 @@ static int mtk_cpufreq_set_target(struct cpufreq_policy *policy,
>  		       policy->cpu);
>  		mtk_cpufreq_set_voltage(info, old_vproc);
>  		WARN_ON(1);
> +		mutex_unlock(&info->lock);
>  		return ret;
>  	}
>  
> @@ -263,6 +270,7 @@ static int mtk_cpufreq_set_target(struct cpufreq_policy *policy,
>  		       policy->cpu);
>  		clk_set_parent(cpu_clk, armpll);
>  		mtk_cpufreq_set_voltage(info, old_vproc);
> +		mutex_unlock(&info->lock);
>  		return ret;
>  	}
>  
> @@ -273,6 +281,7 @@ static int mtk_cpufreq_set_target(struct cpufreq_policy *policy,
>  		       policy->cpu);
>  		mtk_cpufreq_set_voltage(info, inter_vproc);
>  		WARN_ON(1);
> +		mutex_unlock(&info->lock);
>  		return ret;
>  	}
>  
> @@ -288,15 +297,75 @@ static int mtk_cpufreq_set_target(struct cpufreq_policy *policy,
>  			clk_set_parent(cpu_clk, info->inter_clk);
>  			clk_set_rate(armpll, old_freq_hz);
>  			clk_set_parent(cpu_clk, armpll);
> +			mutex_unlock(&info->lock);
>  			return ret;
>  		}
>  	}
>  
> +	info->opp_freq = freq_hz;
> +	mutex_unlock(&info->lock);
> +
>  	return 0;
>  }
>  
>  #define DYNAMIC_POWER "dynamic-power-coefficient"
>  
> +static int mtk_cpufreq_opp_notifier(struct notifier_block *nb,
> +				    unsigned long event, void *data)
> +{
> +	struct dev_pm_opp *opp = data;
> +	struct dev_pm_opp *opp_item;
> +	struct mtk_cpu_dvfs_info *info =
> +		container_of(nb, struct mtk_cpu_dvfs_info, opp_nb);

Do the assignment after all definitions, instead of awkwardly breaking
the line here.

> +	unsigned long freq, volt;
> +	struct cpufreq_policy *policy;
> +	int ret = 0;
> +
> +	if (event == OPP_EVENT_ADJUST_VOLTAGE) {
> +		freq = dev_pm_opp_get_freq(opp);
> +
> +		mutex_lock(&info->lock);
> +		if (info->opp_freq == freq) {
> +			volt = dev_pm_opp_get_voltage(opp);
> +			ret = mtk_cpufreq_set_voltage(info, volt);
> +			if (ret)
> +				dev_err(info->cpu_dev, "failed to scale voltage: %d\n",
> +					ret);
> +		}
> +		mutex_unlock(&info->lock);
> +	} else if (event == OPP_EVENT_DISABLE) {
> +		freq = info->opp_freq;
> +		opp_item = dev_pm_opp_find_freq_ceil(info->cpu_dev, &freq);

name it new_opp instead of opp_item.

> +		if (!IS_ERR(opp_item))
> +			dev_pm_opp_put(opp_item);
> +		else
> +			freq = 0;
> +

What is the purpose of the above code ?

> +		/* case of current opp is disabled */
> +		if (freq == 0 || freq != info->opp_freq) {
> +			// find an enable opp item

Use proper commenting style please.

> +			freq = 1;
> +			opp_item = dev_pm_opp_find_freq_ceil(info->cpu_dev,
> +							     &freq);
> +			if (!IS_ERR(opp_item)) {
> +				dev_pm_opp_put(opp_item);
> +				policy = cpufreq_cpu_get(info->opp_cpu);
> +				if (policy) {
> +					cpufreq_driver_target(policy,
> +						freq / 1000,
> +						CPUFREQ_RELATION_L);

Why don't you simply call this instead of all the code in the else
block ?

> +					cpufreq_cpu_put(policy);
> +				}
> +			} else {
> +				pr_err("%s: all opp items are disabled\n",
> +				       __func__);
> +			}
> +		}
> +	}
> +
> +	return notifier_from_errno(ret);
> +}
> +
>  static int mtk_cpu_dvfs_info_init(struct mtk_cpu_dvfs_info *info, int cpu)
>  {
>  	struct device *cpu_dev;
> @@ -383,11 +452,21 @@ static int mtk_cpu_dvfs_info_init(struct mtk_cpu_dvfs_info *info, int cpu)
>  	info->intermediate_voltage = dev_pm_opp_get_voltage(opp);
>  	dev_pm_opp_put(opp);
>  
> +	info->opp_cpu = cpu;
> +	info->opp_nb.notifier_call = mtk_cpufreq_opp_notifier;
> +	ret = dev_pm_opp_register_notifier(cpu_dev, &info->opp_nb);
> +	if (ret) {
> +		pr_warn("cannot register opp notification\n");
> +		goto out_free_opp_table;
> +	}
> +
> +	mutex_init(&info->lock);
>  	info->cpu_dev = cpu_dev;
>  	info->proc_reg = proc_reg;
>  	info->sram_reg = IS_ERR(sram_reg) ? NULL : sram_reg;
>  	info->cpu_clk = cpu_clk;
>  	info->inter_clk = inter_clk;
> +	info->opp_freq = clk_get_rate(cpu_clk);
>  
>  	/*
>  	 * If SRAM regulator is present, software "voltage tracking" is needed
> -- 
> 2.12.5

-- 
viresh

Re: [v5, PATCH 4/5] cpufreq: mediatek: add opp notification for SVS support

[Viresh Kumar]

On 09-12-19, 14:56, andrew-sh.cheng wrote:
> On Wed, 2019-11-27 at 14:06 +0530, Viresh Kumar wrote:
> > On 26-11-19, 19:50, Andrew-sh.Cheng wrote:
> > > +		if (!IS_ERR(opp_item))
> > > +			dev_pm_opp_put(opp_item);
> > > +		else
> > > +			freq = 0;
> > > +
> > 
> > What is the purpose of the above code ?
> When dev_pm_opp_find_freq_ceil() doesn't find matching opp item, freq
> value won't be set.
> Set it as 0 for below checking
> > 
> > > +		/* case of current opp is disabled */
> > > +		if (freq == 0 || freq != info->opp_freq) {
> > > +			// find an enable opp item
> > > +			freq = 1;
> > > +			opp_item = dev_pm_opp_find_freq_ceil(info->cpu_dev,
> > > +							     &freq);
> > > +			if (!IS_ERR(opp_item)) {
> > > +				dev_pm_opp_put(opp_item);
> > > +				policy = cpufreq_cpu_get(info->opp_cpu);
> > > +				if (policy) {
> > > +					cpufreq_driver_target(policy,
> > > +						freq / 1000,
> > > +						CPUFREQ_RELATION_L);
> > 
> > Why don't you simply call this instead of all the code in the else
> > block ?
> These else code is used to check "current opp item is disabled or not".
> If not, do nothing.
> If current opp item is disabled, need to find an not-disabled opp item,
> and set frequency to it.

Right. So this notifier helper of yours receive the opp which is getting
disabled, why don't you compare its frequency directly to see if the current OPP
is getting disabled ?

-- 
viresh

Re: [v5, PATCH 4/5] cpufreq: mediatek: add opp notification for SVS support

[Viresh Kumar]

On 10-03-20, 16:11, andrew-sh.cheng wrote:
> On Tue, 2019-12-10 at 14:43 +0800, Viresh Kumar wrote:
> > On 09-12-19, 14:56, andrew-sh.cheng wrote:
> > > On Wed, 2019-11-27 at 14:06 +0530, Viresh Kumar wrote:
> > > > On 26-11-19, 19:50, Andrew-sh.Cheng wrote:
> > > > > +		if (!IS_ERR(opp_item))
> > > > > +			dev_pm_opp_put(opp_item);
> > > > > +		else
> > > > > +			freq = 0;
> > > > > +
> > > > 
> > > > What is the purpose of the above code ?
> > > When dev_pm_opp_find_freq_ceil() doesn't find matching opp item, freq
> > > value won't be set.
> > > Set it as 0 for below checking
> > > > 
> > > > > +		/* case of current opp is disabled */
> > > > > +		if (freq == 0 || freq != info->opp_freq) {
> > > > > +			// find an enable opp item
> > > > > +			freq = 1;
> > > > > +			opp_item = dev_pm_opp_find_freq_ceil(info->cpu_dev,
> > > > > +							     &freq);
> > > > > +			if (!IS_ERR(opp_item)) {
> > > > > +				dev_pm_opp_put(opp_item);
> > > > > +				policy = cpufreq_cpu_get(info->opp_cpu);
> > > > > +				if (policy) {
> > > > > +					cpufreq_driver_target(policy,
> > > > > +						freq / 1000,
> > > > > +						CPUFREQ_RELATION_L);
> > > > 
> > > > Why don't you simply call this instead of all the code in the else
> > > > block ?
> > > These else code is used to check "current opp item is disabled or not".
> > > If not, do nothing.
> > > If current opp item is disabled, need to find an not-disabled opp item,
> > > and set frequency to it.
> > 
> > Right. So this notifier helper of yours receive the opp which is getting
> > disabled, why don't you compare its frequency directly to see if the current OPP
> > is getting disabled ?
> Sorry to overlook your question.
> This is because when the opp is disabled,
> we cannot use dev_pm_opp_get_freq() to get frequency of that opp.
> There is a check:
> 	if (IS_ERR_OR_NULL(opp) || !opp->available) {

I think we can remove the available check here, as we are jut trying
to find frequency of an OPP we already have. Send a patch for that
please.

> 		pr_err("%s: Invalid parameters\n", __func__);
> 		return 0;
> 
> > 
> 

-- 
viresh

Re: [v5, PATCH 4/5] cpufreq: mediatek: add opp notification for SVS support

[Viresh Kumar]

On 13-03-20, 15:22, andrew-sh.cheng wrote:
> I have something want to consult you.
> For your previous comment, you suggest use read-write lock to replace
> mutex lock.
> Will it be more efficiently even when all are write lock?
> (all lock region are "setting VProc voltage")

The data to be protected here isn't the VProc voltage but the list of
valid OPPs. My idea was if we can make the target() routine run a bit
faster as it really matters as it is called from scheduler hot path.

It won't be wrong to use the mutex the way you have used it right now,
but I think the read lock is much faster, though the read/write lock
is more beneficial in case where there are multiple readers and fewer
writers. The target() routine gets called multiple times here, not
in parallel, and the OPP change notifier won't be called so often.

-- 
viresh

Re: [v5, PATCH 4/5] cpufreq: mediatek: add opp notification for SVS support

[Viresh Kumar]

On 06-04-20, 17:12, andrew-sh.cheng wrote:
> I will use regulator in the locked region.
> And regulator will use mutex_lock.

Yeah, you can't use spinlock here, use a mutex.

-- 
viresh

Re: [v5, PATCH 4/5] cpufreq: mediatek: add opp notification for SVS support

[Viresh Kumar]

On 07-04-20, 14:54, andrew-sh.cheng wrote:
> On Mon, 2020-04-06 at 14:59 +0530, Viresh Kumar wrote:
> > On 06-04-20, 17:12, andrew-sh.cheng wrote:
> > > I will use regulator in the locked region.
> > > And regulator will use mutex_lock.
> > 
> > Yeah, you can't use spinlock here, use a mutex.
> > 
> Hi Viresh,
> 
> I am not familiar with read/write lock.
> Do you mean there is another read/write function, which is not
> read_lock()/write_lock(), using mutex but not spinlock?

Heh, I am asking you to use simple mutex here, leave the read/write
lock thing completely as it won't work here.

-- 
viresh

Re: [v5, PATCH 2/5] dt-bindings: devfreq: add compatible for mt8183 cci devfreq

[Chanwoo Choi]

Hi,

On 11/26/19 8:50 PM, Andrew-sh.Cheng wrote:
> From: "Andrew-sh.Cheng" <andrew-sh.cheng@mediatek.com>
> 
> This adds dt-binding documentation of cci devfreq
> for Mediatek MT8183 SoC platform.
> 
> Signed-off-by: Andrew-sh.Cheng <andrew-sh.cheng@mediatek.com>
> ---
>  .../bindings/devfreq/mt8183-cci-devfreq.txt          | 20 ++++++++++++++++++++

mt8183-cci.txt is better without 'devfreq' word.

I recommend to make the binding document with yaml.
You can refer to the example[1]
[1] https://git.kernel.org/pub/scm/linux/kernel/git/chanwoo/linux.git/commit/?h=devfreq-next&id=6ad0b4fb960c3bc32034d8f3ec7609c8bcb8d9a4

>  1 file changed, 20 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/devfreq/mt8183-cci-devfreq.txt
> 
> diff --git a/Documentation/devicetree/bindings/devfreq/mt8183-cci-devfreq.txt b/Documentation/devicetree/bindings/devfreq/mt8183-cci-devfreq.txt
> new file mode 100644
> index 000000000000..a65a70bb9f09
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/devfreq/mt8183-cci-devfreq.txt
> @@ -0,0 +1,20 @@
> +* Mediatek Cache Coherent Interconnect(CCI) frequency device

recommend to add the more detailed description 
of what is the role of this driver.

> +
> +Required properties:
> +- compatible: should contain "mediatek,mt8183-cci" for frequency scaling of CCI
> +- clocks: for frequency scaling of CCI
> +- clock-names: for frequency scaling of CCI driver to reference

	

> +- regulator: for voltage scaling of CCI
> +- operating-points-v2: for frequency scaling of CCI opp table
> +
> +Example:
> +	cci: cci {
> +		compatible = "mediatek,mt8183-cci";
> +		clocks = <&apmixedsys CLK_APMIXED_CCIPLL>;
> +		clock-names = "cci_clock";

Recommend to use 'cci' without '_clock' because we can
know that it's clock name event if '_clock'.

> +		operating-points-v2 = <&cci_opp>;
> +	};
> +
> +	&cci {
> +		proc-supply = <&mt6358_vproc12_reg>;
> +	};
> \ No newline at end of file
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics

Re: [v5, PATCH 0/5] Add cpufreq and cci devfreq for mt8183, and SVS support

[Chanwoo Choi]

Hi,

On 11/26/19 8:50 PM, Andrew-sh.Cheng wrote:
> From: "Andrew-sh.Cheng" <andrew-sh.cheng@mediatek.com>
> 
> MT8183 supports CPU DVFS and CCI DVFS, and LITTLE cpus and CCI are in the same voltage domain.
> So, this series is to add drivers to handle the voltage coupling between CPU and CCI DVFS.
> 
> For SVS support, need OPP_EVENT_ADJUST_VOLTAGE and corresponding reaction.

What is correct full word of SVS?
- S(?) VS (Voltage Scaling) ?

> depend on:
> 	https://patchwork.kernel.org/patch/11193513/ 
> 
> Change since v4:
> 	- Remove redundant code
> 
> 
> Andrew-sh.Cheng (5):
>   cpufreq: mediatek: add clock enable for intermediate clock
>   dt-bindings: devfreq: add compatible for mt8183 cci devfreq
>   devfreq: add mediatek cci devfreq
>   cpufreq: mediatek: add opp notification for SVS support
>   devfreq: mediatek: cci devfreq register opp notification for SVS
>     support
> 
>  .../bindings/devfreq/mt8183-cci-devfreq.txt        |  20 ++
>  drivers/cpufreq/mediatek-cpufreq.c                 |  92 +++++-
>  drivers/devfreq/Kconfig                            |  10 +
>  drivers/devfreq/Makefile                           |   1 +
>  drivers/devfreq/mt8183-cci-devfreq.c               | 308 +++++++++++++++++++++
>  5 files changed, 429 insertions(+), 2 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/devfreq/mt8183-cci-devfreq.txt
>  create mode 100644 drivers/devfreq/mt8183-cci-devfreq.c
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics

Re: [v5, PATCH 3/5] devfreq: add mediatek cci devfreq

[Chanwoo Choi]

Hi,

"mtk_cci_vmon" governor looks like the devfreq passive governor.
But, the existing devfreq passive governor depend on the other devfreq device.
"mtk_cci_vmon" governor depend on the regulator with regulator notifier.

I think that it is better to extend the passive governor
in order to support the regulator notifier.
It is possible because passive governor already used
the devfreq notifier. 

Previously, the patch[1] tried to add the cpu based scaling to passive governor.
[1] https://lore.kernel.org/patchwork/patch/1101049/
- [RFC,v2] PM / devfreq: Add cpu based scaling support to passive_governor

Regards,
Chanwoo Choi

On 11/26/19 8:50 PM, Andrew-sh.Cheng wrote:
> From: "Andrew-sh.Cheng" <andrew-sh.cheng@mediatek.com>
> 
> This adds a devfreq driver for the Cache Coherent Interconnect (CCI)
> of the Mediatek MT8183.
> 
> On the MT8183 the CCI is supplied by the same regulator as the LITTLE
> cores. The driver is notified when the regulator voltage changes
> (driven by cpufreq) and adjusts the CCI frequency to the maximum
> possible value.
> 
> Signed-off-by: Andrew-sh.Cheng <andrew-sh.cheng@mediatek.com>
> ---
>  drivers/devfreq/Kconfig              |  10 ++
>  drivers/devfreq/Makefile             |   1 +
>  drivers/devfreq/mt8183-cci-devfreq.c | 247 +++++++++++++++++++++++++++++++++++
>  3 files changed, 258 insertions(+)
>  create mode 100644 drivers/devfreq/mt8183-cci-devfreq.c
> 
> diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
> index defe1d438710..76bc42657787 100644
> --- a/drivers/devfreq/Kconfig
> +++ b/drivers/devfreq/Kconfig
> @@ -92,6 +92,16 @@ config ARM_EXYNOS_BUS_DEVFREQ
>  	  and adjusts the operating frequencies and voltages with OPP support.
>  	  This does not yet operate with optimal voltages.
>  
> +config ARM_MT8183_CCI_DEVFREQ
> +	tristate "MT8183 CCI DEVFREQ Driver"
> +	depends on ARM_MEDIATEK_CPUFREQ
> +	help
> +		This adds a devfreq driver for Cache Coherent Interconnect
> +		of Mediatek MT8183, which is shared the same regulator
> +		with cpu cluster.
> +		It can track buck voltage and update a proper cci frequency.
> +		Use notification to get regulator status.
> +
>  config ARM_TEGRA_DEVFREQ
>  	tristate "NVIDIA Tegra30/114/124/210 DEVFREQ Driver"
>  	depends on ARCH_TEGRA_3x_SOC || ARCH_TEGRA_114_SOC || \
> diff --git a/drivers/devfreq/Makefile b/drivers/devfreq/Makefile
> index 338ae8440db6..1fa05e39e4ff 100644
> --- a/drivers/devfreq/Makefile
> +++ b/drivers/devfreq/Makefile
> @@ -9,6 +9,7 @@ obj-$(CONFIG_DEVFREQ_GOV_PASSIVE)	+= governor_passive.o
>  
>  # DEVFREQ Drivers
>  obj-$(CONFIG_ARM_EXYNOS_BUS_DEVFREQ)	+= exynos-bus.o
> +obj-$(CONFIG_ARM_MT8183_CCI_DEVFREQ)	+= mt8183-cci-devfreq.o
>  obj-$(CONFIG_ARM_RK3399_DMC_DEVFREQ)	+= rk3399_dmc.o
>  obj-$(CONFIG_ARM_TEGRA_DEVFREQ)		+= tegra30-devfreq.o
>  obj-$(CONFIG_ARM_TEGRA20_DEVFREQ)	+= tegra20-devfreq.o
> diff --git a/drivers/devfreq/mt8183-cci-devfreq.c b/drivers/devfreq/mt8183-cci-devfreq.c
> new file mode 100644
> index 000000000000..818a167c442f
> --- /dev/null
> +++ b/drivers/devfreq/mt8183-cci-devfreq.c
> @@ -0,0 +1,247 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2019 MediaTek Inc.
> +
> + * Author: Andrew-sh.Cheng <andrew-sh.cheng@mediatek.com>
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/devfreq.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/regulator/consumer.h>
> +
> +#include "governor.h"
> +
> +struct cci_devfreq {
> +	struct devfreq *devfreq;
> +	struct regulator *proc_reg;
> +	unsigned long proc_reg_uV;																																																																																															
> +	struct clk *cci_clk;
> +	struct notifier_block nb;
> +};
> +
> +static int cci_devfreq_regulator_notifier(struct notifier_block *nb,
> +					  unsigned long val, void *data)
> +{
> +	int ret;
> +	struct cci_devfreq *cci_df =
> +		container_of(nb, struct cci_devfreq, nb);
> +
> +	/* deal with reduce frequency */
> +	if (val & REGULATOR_EVENT_PRE_VOLTAGE_CHANGE) {
> +		struct pre_voltage_change_data *pvc_data = data;
> +
> +		if (pvc_data->min_uV < pvc_data->old_uV) {
> +			cci_df->proc_reg_uV =
> +				(unsigned long)(pvc_data->min_uV);
> +			mutex_lock(&cci_df->devfreq->lock);
> +			ret = update_devfreq(cci_df->devfreq);
> +			if (ret)
> +				pr_err("Fail to reduce cci frequency: %d\n",
> +				       ret);
> +			mutex_unlock(&cci_df->devfreq->lock);
> +		}
> +	} else if ((val & REGULATOR_EVENT_ABORT_VOLTAGE_CHANGE) &&
> +	    ((unsigned long)data > cci_df->proc_reg_uV)) {
> +		cci_df->proc_reg_uV = (unsigned long)data;
> +		mutex_lock(&cci_df->devfreq->lock);
> +		ret = update_devfreq(cci_df->devfreq);
> +		if (ret)
> +			pr_err("Fail to raise cci frequency back: %d\n", ret);
> +		mutex_unlock(&cci_df->devfreq->lock);
> +	} else if ((val & REGULATOR_EVENT_VOLTAGE_CHANGE) &&
> +	    (cci_df->proc_reg_uV < (unsigned long)data)) {
> +		/* deal with increase frequency */
> +		cci_df->proc_reg_uV = (unsigned long)data;
> +		mutex_lock(&cci_df->devfreq->lock);
> +		ret = update_devfreq(cci_df->devfreq);
> +		if (ret)
> +			pr_err("Fail to raise cci frequency: %d\n", ret);
> +		mutex_unlock(&cci_df->devfreq->lock);
> +	}
> +
> +	return 0;
> +}
> +
> +static int mtk_cci_governor_get_target(struct devfreq *devfreq,
> +				       unsigned long *freq)
> +{
> +	struct cci_devfreq *cci_df;
> +	struct dev_pm_opp *opp;
> +
> +	cci_df = dev_get_drvdata(devfreq->dev.parent);
> +
> +	/* find available frequency */
> +	opp = dev_pm_opp_find_freq_ceil_by_volt(devfreq->dev.parent,
> +						cci_df->proc_reg_uV);
> +	*freq = dev_pm_opp_get_freq(opp);
> +
> +	return 0;
> +}
> +
> +static int mtk_cci_governor_event_handler(struct devfreq *devfreq,
> +					  unsigned int event, void *data)
> +{
> +	int ret;
> +	struct cci_devfreq *cci_df;
> +	struct notifier_block *nb;
> +
> +	cci_df = dev_get_drvdata(devfreq->dev.parent);
> +	nb = &cci_df->nb;
> +
> +	switch (event) {
> +	case DEVFREQ_GOV_START:
> +	case DEVFREQ_GOV_RESUME:
> +		nb->notifier_call = cci_devfreq_regulator_notifier;
> +		ret = regulator_register_notifier(cci_df->proc_reg,
> +						  nb);
> +		if (ret)
> +			pr_err("%s: failed to add governor: %d\n", __func__,
> +			       ret);
> +		break;
> +
> +	case DEVFREQ_GOV_STOP:
> +	case DEVFREQ_GOV_SUSPEND:
> +		ret = regulator_unregister_notifier(cci_df->proc_reg,
> +						    nb);
> +		if (ret)
> +			pr_err("%s: failed to add governor: %d\n", __func__,
> +			       ret);
> +		break;
> +
> +	default:
> +		break;
> +	}
> +
> +	return 0;
> +}
> +
> +static struct devfreq_governor mtk_cci_devfreq_governor = {
> +	.name = "mtk_cci_vmon",
> +	.get_target_freq = mtk_cci_governor_get_target,
> +	.event_handler = mtk_cci_governor_event_handler,
> +	.immutable = true
> +};
> +
> +static int mtk_cci_devfreq_target(struct device *dev, unsigned long *freq,
> +				  u32 flags)
> +{
> +	int ret;
> +	struct cci_devfreq *cci_df = dev_get_drvdata(dev);
> +
> +	if (!cci_df)
> +		return -EINVAL;
> +
> +	ret = clk_set_rate(cci_df->cci_clk, *freq);
> +	if (ret) {
> +		pr_err("%s: failed cci to set rate: %d\n", __func__,
> +		       ret);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static struct devfreq_dev_profile cci_devfreq_profile = {
> +	.target = mtk_cci_devfreq_target,
> +};
> +
> +static int mtk_cci_devfreq_probe(struct platform_device *pdev)
> +{
> +	struct device *cci_dev = &pdev->dev;
> +	struct cci_devfreq *cci_df;
> +	int ret;
> +
> +	cci_df = devm_kzalloc(cci_dev, sizeof(*cci_df), GFP_KERNEL);
> +	if (!cci_df)
> +		return -ENOMEM;
> +
> +	cci_df->cci_clk = devm_clk_get(cci_dev, "cci_clock");
> +	ret = PTR_ERR_OR_ZERO(cci_df->cci_clk);
> +	if (ret) {
> +		if (ret != -EPROBE_DEFER)
> +			dev_err(cci_dev, "failed to get clock for CCI: %d\n",
> +				ret);
> +		return ret;
> +	}
> +	cci_df->proc_reg = devm_regulator_get_optional(cci_dev, "proc");
> +	ret = PTR_ERR_OR_ZERO(cci_df->proc_reg);
> +	if (ret) {
> +		if (ret != -EPROBE_DEFER)
> +			dev_err(cci_dev, "failed to get regulator for CCI: %d\n",
> +				ret);
> +		return ret;
> +	}
> +
> +	ret = dev_pm_opp_of_add_table(cci_dev);
> +	if (ret) {
> +		dev_err(cci_dev, "Fail to init CCI OPP table: %d\n", ret);
> +		return ret;
> +	}
> +
> +	platform_set_drvdata(pdev, cci_df);
> +
> +	cci_df->devfreq = devm_devfreq_add_device(cci_dev,
> +						  &cci_devfreq_profile,
> +						  "mtk_cci_vmon",
> +						  NULL);
> +	if (IS_ERR(cci_df->devfreq)) {
> +		ret = PTR_ERR(cci_df->devfreq);
> +		dev_err(cci_dev, "cannot create cci devfreq device:%d\n", ret);
> +		dev_pm_opp_of_remove_table(cci_dev);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static const __maybe_unused struct of_device_id
> +	mediatek_cci_devfreq_of_match[] = {
> +	{ .compatible = "mediatek,mt8183-cci" },
> +	{ },
> +};
> +MODULE_DEVICE_TABLE(of, mediatek_cci_devfreq_of_match);
> +
> +static struct platform_driver cci_devfreq_driver = {
> +	.probe	= mtk_cci_devfreq_probe,
> +	.driver = {
> +		.name = "mediatek-cci-devfreq",
> +		.of_match_table = of_match_ptr(mediatek_cci_devfreq_of_match),
> +	},
> +};
> +
> +static int __init mtk_cci_devfreq_init(void)
> +{
> +	int ret;
> +
> +	ret = devfreq_add_governor(&mtk_cci_devfreq_governor);
> +	if (ret) {
> +		pr_err("%s: failed to add governor: %d\n", __func__, ret);
> +		return ret;
> +	}
> +
> +	ret = platform_driver_register(&cci_devfreq_driver);
> +	if (ret)
> +		devfreq_remove_governor(&mtk_cci_devfreq_governor);
> +
> +	return ret;
> +}
> +module_init(mtk_cci_devfreq_init)

Use module_platform_driver

> +
> +static void __exit mtk_cci_devfreq_exit(void)
> +{
> +	int ret;
> +
> +	ret = devfreq_remove_governor(&mtk_cci_devfreq_governor);
> +	if (ret)
> +		pr_err("%s: failed to remove governor: %d\n", __func__, ret);
> +
> +	platform_driver_unregister(&cci_devfreq_driver);
> +}
> +module_exit(mtk_cci_devfreq_exit)
> +
> +MODULE_DESCRIPTION("Mediatek CCI devfreq driver");
> +MODULE_AUTHOR("Andrew-sh.Cheng <andrew-sh.cheng@mediatek.com>");
> +MODULE_LICENSE("GPL v2");
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics