Message-id: <579F2445.1020200@samsung.com>
Date:	Mon, 01 Aug 2016 19:28:21 +0900
From:	Chanwoo Choi <cw00.choi@...sung.com>
To:	Lin Huang <hl@...k-chips.com>, heiko@...ech.de
Cc:	tixy@...aro.org, dbasehore@...omium.org, airlied@...ux.ie,
	mturquette@...libre.com, typ@...k-chips.com, sboyd@...eaurora.org,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	dianders@...omium.org, linux-rockchip@...ts.infradead.org,
	kyungmin.park@...sung.com, myungjoo.ham@...sung.com,
	linux-arm-kernel@...ts.infradead.org, mark.yao@...k-chips.com
Subject: Re: [PATCH v4 6/7] PM / devfreq: rockchip: add devfreq driver for
 rk3399 dmc

Hi Lin,

As I mentioned on patch5, you better to make the documentation as following: 
- Documentation/devicetree/bindings/devfreq/rk3399_dmc.txt
And, I add the comments.


On 2016년 07월 29일 16:57, Lin Huang wrote:
> base on dfi result, we do ddr frequency scaling, register
> dmc driver to devfreq framework, and use simple-ondemand
> policy.
> 
> Signed-off-by: Lin Huang <hl@...k-chips.com>
> ---
> Changes in v4:
> - use arm_smccc_smc() function talk to bl31
> - delete rockchip_dmc.c file and config
> - delete dmc_notify
> - adjust probe order
>  
> Changes in v3:
> - operate dram setting through sip call
> - imporve set rate flow
> 
> Changes in v2:
> - None
>  
> Changes in v1:
> - move dfi controller to event
> - fix set voltage sequence when set rate fail
> - change Kconfig type from tristate to bool
> - move unuse EXPORT_SYMBOL_GPL()
> 
>  drivers/devfreq/Kconfig               |   1 +
>  drivers/devfreq/Makefile              |   1 +
>  drivers/devfreq/rockchip/Kconfig      |   8 +
>  drivers/devfreq/rockchip/Makefile     |   1 +
>  drivers/devfreq/rockchip/rk3399_dmc.c | 473 ++++++++++++++++++++++++++++++++++
>  5 files changed, 484 insertions(+)
>  create mode 100644 drivers/devfreq/rockchip/Kconfig
>  create mode 100644 drivers/devfreq/rockchip/Makefile
>  create mode 100644 drivers/devfreq/rockchip/rk3399_dmc.c
> 
> diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
> index 64281bb..acb2a57 100644
> --- a/drivers/devfreq/Kconfig
> +++ b/drivers/devfreq/Kconfig
> @@ -99,5 +99,6 @@ config ARM_TEGRA_DEVFREQ
>           operating frequencies and voltages with OPP support.
>  
>  source "drivers/devfreq/event/Kconfig"
> +source "drivers/devfreq/rockchip/Kconfig"

This patch include the only one patch. So, I think that
you don't need to create the 'rockchip' directory.

>  
>  endif # PM_DEVFREQ
> diff --git a/drivers/devfreq/Makefile b/drivers/devfreq/Makefile
> index 5134f9e..d844e23 100644
> --- a/drivers/devfreq/Makefile
> +++ b/drivers/devfreq/Makefile
> @@ -9,6 +9,7 @@ obj-$(CONFIG_DEVFREQ_GOV_USERSPACE)	+= governor_userspace.o
>  obj-$(CONFIG_ARM_EXYNOS4_BUS_DEVFREQ)	+= exynos/
>  obj-$(CONFIG_ARM_EXYNOS5_BUS_DEVFREQ)	+= exynos/
>  obj-$(CONFIG_ARM_TEGRA_DEVFREQ)		+= tegra-devfreq.o
> +obj-$(CONFIG_ARCH_ROCKCHIP)		+= rockchip/

ditto.

>  
>  # DEVFREQ Event Drivers
>  obj-$(CONFIG_PM_DEVFREQ_EVENT)		+= event/
> diff --git a/drivers/devfreq/rockchip/Kconfig b/drivers/devfreq/rockchip/Kconfig
> new file mode 100644
> index 0000000..d8f9e66
> --- /dev/null
> +++ b/drivers/devfreq/rockchip/Kconfig
> @@ -0,0 +1,8 @@
> +config ARM_RK3399_DMC_DEVFREQ
> +	tristate "ARM RK3399 DMC DEVFREQ Driver"
> +	select PM_OPP
> +	select DEVFREQ_GOV_SIMPLE_ONDEMAND
> +	help
> +          This adds the DEVFREQ driver for the RK3399 dmc. It sets the frequency

If you add the full description for 'dmc' as following,
it is easy to understand the operation of this device driver.
- DMC (Dynamic Memory Controller)

> +          for the memory controller and reads the usage counts from hardware.
> +
> diff --git a/drivers/devfreq/rockchip/Makefile b/drivers/devfreq/rockchip/Makefile
> new file mode 100644
> index 0000000..c62c105
> --- /dev/null
> +++ b/drivers/devfreq/rockchip/Makefile
> @@ -0,0 +1 @@
> +obj-$(CONFIG_ARM_RK3399_DMC_DEVFREQ)	+= rk3399_dmc.o
> diff --git a/drivers/devfreq/rockchip/rk3399_dmc.c b/drivers/devfreq/rockchip/rk3399_dmc.c
> new file mode 100644
> index 0000000..527aa11
> --- /dev/null
> +++ b/drivers/devfreq/rockchip/rk3399_dmc.c
> @@ -0,0 +1,473 @@
> +/*
> + * Copyright (c) 2016, Fuzhou Rockchip Electronics Co., Ltd

You miss the '.' at the end of the copylight. 
When you use an abbreviation, you should add '.' for Ltd.
- s/Ltd/Ltd.


> + * Author: Lin Huang <hl@...k-chips.com>
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms and conditions of the GNU General Public License,
> + * version 2, as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + */
> +
> +#include <linux/arm-smccc.h>
> +#include <linux/clk.h>
> +#include <linux/completion.h>

You don't need to include the "completion.h".
Without "completion.h", the build is working.

> +#include <linux/delay.h>
> +#include <linux/devfreq.h>
> +#include <linux/devfreq-event.h>
> +#include <linux/interrupt.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/pm_opp.h>
> +#include <linux/regulator/consumer.h>
> +#include <linux/rwsem.h>
> +#include <linux/suspend.h>
> +#include <linux/syscore_ops.h>

You don't need to include the "syscore_ops.h".
Without "syscore_ops.h", the build is working.

> +
> +#include <soc/rockchip/rockchip_sip.h>
> +
> +struct dram_timing {
> +	unsigned int ddr3_speed_bin;
> +	unsigned int pd_idle;
> +	unsigned int sr_idle;
> +	unsigned int sr_mc_gate_idle;
> +	unsigned int srpd_lite_idle;
> +	unsigned int standby_idle;
> +	unsigned int dram_dll_dis_freq;
> +	unsigned int phy_dll_dis_freq;
> +	unsigned int ddr3_odt_dis_freq;
> +	unsigned int ddr3_drv;
> +	unsigned int ddr3_odt;
> +	unsigned int phy_ddr3_ca_drv;
> +	unsigned int phy_ddr3_dq_drv;
> +	unsigned int phy_ddr3_odt;
> +	unsigned int lpddr3_odt_dis_freq;
> +	unsigned int lpddr3_drv;
> +	unsigned int lpddr3_odt;
> +	unsigned int phy_lpddr3_ca_drv;
> +	unsigned int phy_lpddr3_dq_drv;
> +	unsigned int phy_lpddr3_odt;
> +	unsigned int lpddr4_odt_dis_freq;
> +	unsigned int lpddr4_drv;
> +	unsigned int lpddr4_dq_odt;
> +	unsigned int lpddr4_ca_odt;
> +	unsigned int phy_lpddr4_ca_drv;
> +	unsigned int phy_lpddr4_ck_cs_drv;
> +	unsigned int phy_lpddr4_dq_drv;
> +	unsigned int phy_lpddr4_odt;
> +};

The dram_timing is used for SMC (Secure Monitor Call)? 
I recommend that you add the detailed description about this property
on Documentation.

> +
> +struct rk3399_dmcfreq {
> +	struct device *dev;
> +	struct devfreq *devfreq;
> +	struct devfreq_simple_ondemand_data ondemand_data;
> +	struct clk *dmc_clk;
> +	struct devfreq_event_dev *edev;
> +	struct mutex lock;
> +	struct dram_timing *timing;
> +	wait_queue_head_t	wait_dcf_queue;
> +	int irq;
> +	int wait_dcf_flag;

I want to add the full name and description of 'dcf'.
It is unknown word.

> +	struct regulator *vdd_center;
> +	unsigned long rate, target_rate;
> +	unsigned long volt, target_volt;

I think that if you add 'curr_opp' variable,
you can reduce the calling of devfreq_recommended_opp() in rk3399_dmcfreq_target()
	struct dev_pm_opp *curr_opp;

> +};
> +
> +static int rk3399_dmcfreq_target(struct device *dev, unsigned long *freq,
> +				 u32 flags)
> +{
> +	struct platform_device *pdev = container_of(dev, struct platform_device,
> +						    dev);
> +	struct rk3399_dmcfreq *dmcfreq = platform_get_drvdata(pdev);

You can use the 'dev_get_drvdata()' to simplify it instead of 'platform_get_drvdata()'.

	struct rk3399_dmcfreq *dmcfreq = dev_get_drvdata(dev);

> +	struct dev_pm_opp *opp;
> +	unsigned long old_clk_rate = dmcfreq->rate;
> +	unsigned long target_volt, target_rate;
> +	int err;
> +
> +	rcu_read_lock();
> +	opp = devfreq_recommended_opp(dev, freq, flags);
> +	if (IS_ERR(opp)) {
> +		rcu_read_unlock();
> +		return PTR_ERR(opp);
> +	}
> +
> +	target_rate = dev_pm_opp_get_freq(opp);
> +	target_volt = dev_pm_opp_get_voltage(opp);
> +	opp = devfreq_recommended_opp(dev, &dmcfreq->rate, flags);
> +	if (IS_ERR(opp)) {
> +		rcu_read_unlock();
> +		return PTR_ERR(opp);
> +	}
> +	dmcfreq->volt = dev_pm_opp_get_voltage(opp);

If you add the 'curr_opp' variable to struct rk3399_dmcfreq,
you can remove the calling of devfreq_recommended_opp().
	dmcfreq->rate = dev_pm_opp_get_freq(dmcfreq->curr_opp);
	dmcfreq->volt = dev_pm_opp_get_freq(dmcfreq->curr_opp);

Because the current rate and voltage is already decided on previous polling cycle,
So we don't need to get the opp with devfreq_recommended_opp().

> +	rcu_read_unlock();
> +
> +	if (dmcfreq->rate == target_rate)
> +		return 0;
> +
> +	mutex_lock(&dmcfreq->lock);
> +
> +	/*
> +	 * if frequency scaling from low to high, adjust voltage first;
> +	 * if frequency scaling from high to low, adjuset frequency first;
> +	 */

s/adjuset/adjust

I recommend that you use a captital letter for first character and use the '.'
instead of ';'.

> +	if (old_clk_rate < target_rate) {
> +		err = regulator_set_voltage(dmcfreq->vdd_center, target_volt,
> +					    target_volt);
> +		if (err) {
> +			dev_err(dev, "Unable to set vol %lu\n", target_volt);

To readability, you better to use the corrent word to pass the precise the log message.
- s/vol/voltage

And, this patch uses the 'Unable to' or 'Cannot' to show the error log.
I recommend that you use the consistent expression if there is not any specific reason.

	dev_err(dev, "Cannot set the voltage %lu uV\n", target_volt);

> +			goto out;
> +		}
> +	}
> +	dmcfreq->wait_dcf_flag = 1;
> +	err = clk_set_rate(dmcfreq->dmc_clk, target_rate);
> +	if (err) {
> +		dev_err(dev,
> +			"Unable to set freq %lu. Current freq %lu. Error %d\n",
> +			target_rate, old_clk_rate, err);

	dev_err(dev, "Cannot set the frequency %lu (%d)\n", target_rate, err);

> +		regulator_set_voltage(dmcfreq->vdd_center, dmcfreq->volt,
> +				      dmcfreq->volt);
> +		goto out;
> +	}
> +
> +	/*
> +	 * wait until bcf irq happen, it means freq scaling finish in bl31,

ditto.

> +	 * use 100ms as timeout time

s/time/time.

> +	 */
> +	if (!wait_event_timeout(dmcfreq->wait_dcf_queue,
> +				!dmcfreq->wait_dcf_flag, HZ / 10))
> +		dev_warn(dev, "Timeout waiting for dcf irq\n");

If the timeout happen, are there any problem?

After setting the frequency and voltage, store the current opp entry on .curr_opp.
	dmcfreq->curr_opp = opp;

> +	/*
> +	 * check the dpll rate
> +	 * there only two result we will get,
> +	 * 1. ddr frequency scaling fail, we still get the old rate
> +	 * 2, ddr frequency scaling sucessful, we get the rate we set
> +	 */
> +	dmcfreq->rate = clk_get_rate(dmcfreq->dmc_clk);
> +
> +	/* if get the incorrect rate, set voltage to old value */
> +	if (dmcfreq->rate != target_rate) {
> +		dev_err(dev, "get wrong ddr frequency, Request freq %lu,\
> +			Current freq %lu\n", target_rate, dmcfreq->rate);
> +		regulator_set_voltage(dmcfreq->vdd_center, dmcfreq->volt,
> +				      dmcfreq->volt);

[Without force, it is just my opion about this code:]
I think that this checking code it is un-needed.
If this case occur, the rk3399_dmc.c never set the specific frequency
because the rk3399 clock don't support the specific frequency for rk3399 dmc.

If you want to set the correct frequency,
When verifying the rk3399 dmc driver, you should check the rk3399 clock driver.

Basically, if the the clock driver don't support the correct same frequency ,
CCF(Common Clock Framework) set the close frequency. It is not a bad thing.


> +	} else if (old_clk_rate > target_rate)
> +		err = regulator_set_voltage(dmcfreq->vdd_center, target_volt,
> +					    target_volt);
> +	if (err)
> +		dev_err(dev, "Unable to set vol %lu\n", target_volt);
	
ditto. You better to use the consistent expression for error log as following:
	dev_err(dev, "Cannot set the voltage %lu uV\n", target_volt);


> +
> +out:
> +	mutex_unlock(&dmcfreq->lock);
> +	return err;
> +}
> +
> +static int rk3399_dmcfreq_get_dev_status(struct device *dev,
> +					 struct devfreq_dev_status *stat)
> +{
> +	struct platform_device *pdev = container_of(dev, struct platform_device,
> +						    dev);
> +	struct rk3399_dmcfreq *dmcfreq = platform_get_drvdata(pdev);
> +	struct devfreq_event_data edata;

ditto. Use the dev_get_drvdata(dev).

> +
> +	devfreq_event_get_event(dmcfreq->edev, &edata);

You need to check the return value for exception handling.

> +
> +	stat->current_frequency = dmcfreq->rate;
> +	stat->busy_time = edata.load_count;
> +	stat->total_time = edata.total_count;
> +
> +	return 0;
> +}
> +
> +static int rk3399_dmcfreq_get_cur_freq(struct device *dev, unsigned long *freq)
> +{
> +	struct platform_device *pdev = container_of(dev, struct platform_device,
> +						    dev);
> +	struct rk3399_dmcfreq *dmcfreq = platform_get_drvdata(pdev);

ditto. Use the dev_get_drvdata(dev).

> +
> +	*freq = dmcfreq->rate;
> +
> +	return 0;
> +}
> +
> +static void rk3399_dmcfreq_exit(struct device *dev)
> +{
> +	struct platform_device *pdev = container_of(dev,
> +						    struct platform_device,
> +						    dev);
> +	struct rk3399_dmcfreq *dmcfreq = platform_get_drvdata(pdev);
> +
> +	devfreq_unregister_opp_notifier(dev, dmcfreq->devfreq);

Use the devm_devfreq_register_opp_notifier(). You don't need to handle it.

> +}
> +
> +static struct devfreq_dev_profile rk3399_devfreq_dmc_profile = {
> +	.polling_ms	= 200,
> +	.target		= rk3399_dmcfreq_target,
> +	.get_dev_status	= rk3399_dmcfreq_get_dev_status,
> +	.get_cur_freq	= rk3399_dmcfreq_get_cur_freq,
> +	.exit		= rk3399_dmcfreq_exit,
> +};
> +
> +static __maybe_unused int rk3399_dmcfreq_suspend(struct device *dev)
> +{
> +	struct platform_device *pdev = container_of(dev,
> +						    struct platform_device,
> +						    dev);
> +	struct rk3399_dmcfreq *dmcfreq = platform_get_drvdata(pdev);

ditto. Use the dev_get_drvdata(dev).

> +
> +	devfreq_event_disable_edev(dmcfreq->edev);
> +	devfreq_suspend_device(dmcfreq->devfreq);

ditto. you need to check the return value.

> +
> +	return 0;
> +}
> +
> +static __maybe_unused int rk3399_dmcfreq_resume(struct device *dev)
> +{
> +	struct platform_device *pdev = container_of(dev,
> +						    struct platform_device,
> +						    dev);
> +	struct rk3399_dmcfreq *dmcfreq = platform_get_drvdata(pdev);

ditto.

> +
> +	devfreq_event_enable_edev(dmcfreq->edev);
> +	devfreq_resume_device(dmcfreq->devfreq);

ditto.

> +
> +	return 0;
> +}
> +
> +static SIMPLE_DEV_PM_OPS(rk3399_dmcfreq_pm, rk3399_dmcfreq_suspend,
> +			 rk3399_dmcfreq_resume);
> +
> +static irqreturn_t rk3399_dmc_irq(int irq, void *dev_id)
> +{
> +	struct rk3399_dmcfreq *dmcfreq = dev_id;
> +	struct arm_smccc_res res;
> +
> +	dmcfreq->wait_dcf_flag = 0;
> +	wake_up(&dmcfreq->wait_dcf_queue);
> +
> +	/* clr dcf irq */

s/ clr dcf irq -> "Clear the DCF Interrupt"

> +	arm_smccc_smc(SIP_DDR_FREQ, 0, 0, CONFIG_DRAM_CLR_IRQ,
> +		      0, 0, 0, 0, &res);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static int of_do_get_timing(struct device_node *np,
> +		struct dram_timing *timing)
> +{
> +	int ret;
> +
> +	ret = of_property_read_u32(np, "ddr3_speed_bin",
> +				   &timing->ddr3_speed_bin);
> +	ret |= of_property_read_u32(np, "pd_idle", &timing->pd_idle);
> +	ret |= of_property_read_u32(np, "sr_idle", &timing->sr_idle);
> +	ret |= of_property_read_u32(np, "sr_mc_gate_idle",
> +				    &timing->sr_mc_gate_idle);
> +	ret |= of_property_read_u32(np, "srpd_lite_idle",
> +				    &timing->srpd_lite_idle);
> +	ret |= of_property_read_u32(np, "standby_idle", &timing->standby_idle);
> +	ret |= of_property_read_u32(np, "dram_dll_dis_freq",
> +				    &timing->dram_dll_dis_freq);
> +	ret |= of_property_read_u32(np, "phy_dll_dis_freq",
> +				    &timing->phy_dll_dis_freq);
> +	ret |= of_property_read_u32(np, "ddr3_odt_dis_freq",
> +				    &timing->ddr3_odt_dis_freq);
> +	ret |= of_property_read_u32(np, "ddr3_drv", &timing->ddr3_drv);
> +	ret |= of_property_read_u32(np, "ddr3_odt", &timing->ddr3_odt);
> +	ret |= of_property_read_u32(np, "phy_ddr3_ca_drv",
> +				    &timing->phy_ddr3_ca_drv);
> +	ret |= of_property_read_u32(np, "phy_ddr3_dq_drv",
> +				    &timing->phy_ddr3_dq_drv);
> +	ret |= of_property_read_u32(np, "phy_ddr3_odt", &timing->phy_ddr3_odt);
> +	ret |= of_property_read_u32(np, "lpddr3_odt_dis_freq",
> +				    &timing->lpddr3_odt_dis_freq);
> +	ret |= of_property_read_u32(np, "lpddr3_drv", &timing->lpddr3_drv);
> +	ret |= of_property_read_u32(np, "lpddr3_odt", &timing->lpddr3_odt);
> +	ret |= of_property_read_u32(np, "phy_lpddr3_ca_drv",
> +				    &timing->phy_lpddr3_ca_drv);
> +	ret |= of_property_read_u32(np, "phy_lpddr3_dq_drv",
> +				    &timing->phy_lpddr3_dq_drv);
> +	ret |= of_property_read_u32(np, "phy_lpddr3_odt",
> +				    &timing->phy_lpddr3_odt);
> +	ret |= of_property_read_u32(np, "lpddr4_odt_dis_freq",
> +				    &timing->lpddr4_odt_dis_freq);
> +	ret |= of_property_read_u32(np, "lpddr4_drv",
> +				    &timing->lpddr4_drv);
> +	ret |= of_property_read_u32(np, "lpddr4_dq_odt",
> +				    &timing->lpddr4_dq_odt);
> +	ret |= of_property_read_u32(np, "lpddr4_ca_odt",
> +				    &timing->lpddr4_ca_odt);
> +	ret |= of_property_read_u32(np, "phy_lpddr4_ca_drv",
> +				    &timing->phy_lpddr4_ca_drv);
> +	ret |= of_property_read_u32(np, "phy_lpddr4_ck_cs_drv",
> +				    &timing->phy_lpddr4_ck_cs_drv);
> +	ret |= of_property_read_u32(np, "phy_lpddr4_dq_drv",
> +				    &timing->phy_lpddr4_dq_drv);
> +	ret |= of_property_read_u32(np, "phy_lpddr4_odt",
> +				    &timing->phy_lpddr4_odt);
> +
> +	return ret;
> +}
> +
> +static struct dram_timing *of_get_ddr_timings(struct device *dev,
> +					      struct device_node *np)
> +{
> +	struct dram_timing	*timing = NULL;
> +	struct device_node	*np_tim;
> +
> +	np_tim = of_parse_phandle(np, "ddr_timing", 0);

As I already mentioned, you need to add the detailed documetation about the property.

> +	if (np_tim) {
> +		timing = devm_kzalloc(dev, sizeof(*timing), GFP_KERNEL);
> +		if (!timing)
> +			goto err;
> +		if (of_do_get_timing(np_tim, timing)) {

I recommend that you better to squash following two functions
because of_do_get_timing() is not used on other point of this driver.
- of_do_get_timing()
- of_get_ddr_timings()

> +			devm_kfree(dev, timing);
> +			goto err;
> +		}

You're missing the 'of_node_put'.
		of_node_put(np_tim);

> +		return timing;
> +	}
> +
> +err:
> +	if (timing) {
> +		devm_kfree(dev, timing);
> +		timing = NULL;
> +	}
> +

ditto.
	of_node_put(np_tim);

> +	return timing;
> +}
> +
> +static int rk3399_dmcfreq_probe(struct platform_device *pdev)
> +{
> +	struct arm_smccc_res res;
> +	struct device *dev = &pdev->dev;
> +	struct device_node *np = pdev->dev.of_node;
> +	uint64_t param = 0;
> +	struct rk3399_dmcfreq *data;
> +	int ret, irq, index;
> +	uint32_t *timing;
> +
> +	irq = platform_get_irq(pdev, 0);
> +	if (irq < 0) {
> +		dev_err(&pdev->dev, "no dmc irq resource\n");

We need to maintain the consistent expression for error log.
		dev_err(&pdev->dev, ""Cannot get the interrupt resource"\n");
		
> +		return -EINVAL;
> +	}
> +	data = devm_kzalloc(dev, sizeof(struct rk3399_dmcfreq), GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	mutex_init(&data->lock);
> +
> +	data->vdd_center = devm_regulator_get(dev, "center");
> +	if (IS_ERR(data->vdd_center)) {
> +		dev_err(dev, "Cannot get the regulator \"center\"\n");
> +		return PTR_ERR(data->vdd_center);
> +	}
> +
> +	data->dmc_clk = devm_clk_get(dev, "dmc_clk");
> +	if (IS_ERR(data->dmc_clk)) {
> +		dev_err(dev, "Cannot get the clk dmc_clk\n");
> +		return PTR_ERR(data->dmc_clk);
> +	};
> +
> +	data->irq = irq;
> +	ret = devm_request_irq(dev, irq, rk3399_dmc_irq, 0,
> +			       dev_name(dev), data);
> +	if (ret) {
> +		dev_err(dev, "failed to request dmc irq: %d\n", ret);

ditto. "Failed to request the dmc irq" or "Cannot request the dmc irq"

> +		return ret;
> +	}
> +
> +	/* get dram timing and pass it to bl31 */

I want to add the more detailed description why this code is necessary.
Because the SMC is usually black box. So, If you add the more explanation,
it help people to understand this code. 

> +	data->timing = of_get_ddr_timings(dev, np);
> +	if (data->timing) {
> +		timing = (uint32_t *)data->timing;
> +		for (index = 0; index < (sizeof(struct dram_timing) / 4);
> +		     index++) {

You better to use following code. It is better way to use
the only one line for 'for' statement.

		size = sizeof(struct dram_timing) / 4;
		for (index = 0; index < size; index++) {

> +			param = index;
> +			param = param << 32 | *timing++;
> +			arm_smccc_smc(SIP_DDR_FREQ, param, 0,
> +				      CONFIG_DRAM_SET_PARAM, 0, 0, 0, 0, &res);
> +			if (res.a0) {
> +				dev_err(dev, "failed to set dram param: %ld\n",
> +					res.a0);
> +				return -EINVAL;
> +			}
> +			param = 0;
> +		}
> +	}
> +
> +	arm_smccc_smc(SIP_DDR_FREQ, 0, 0, CONFIG_DRAM_INIT,
> +		      0, 0, 0, 0, &res);

ditto. You need to add the description.

> +
> +	init_waitqueue_head(&data->wait_dcf_queue);
> +	data->wait_dcf_flag = 0;
> +
> +	data->edev = devfreq_event_get_edev_by_phandle(dev, 0);
> +	if (IS_ERR(data->edev))
> +		return -EPROBE_DEFER;
> +
> +	ret = devfreq_event_enable_edev(data->edev);
> +	if (ret < 0) {
> +		dev_err(dev, "failed to enable devfreq-event devices\n");

s/failed/Failed. Use a capital letter for the first char.

> +		return ret;
> +	}
> +
> +	/*
> +	 * We add a devfreq driver to our parent since it has a device tree node
> +	 * with operating points.
> +	 */

You should wrap the rcu lock before calling the dev_pm_opp_of_add_table().

> +	if (dev_pm_opp_of_add_table(dev)) {
> +		dev_err(dev, "Invalid operating-points in device tree.\n");
> +		return -EINVAL;
> +	}
> +	of_property_read_u32(np, "upthreshold",
> +			     &data->ondemand_data.upthreshold);
> +	of_property_read_u32(np, "downdifferential",
> +			     &data->ondemand_data.downdifferential);

Need one blank line.
Maybe this code to get the properfy for ondemand governor,
the devfreq will support in the future.

> +	data->rate = clk_get_rate(data->dmc_clk);
> +	rk3399_devfreq_dmc_profile.initial_freq = data->rate;

Need one blank line.

> +	data->devfreq = devfreq_add_device(dev,
> +					   &rk3399_devfreq_dmc_profile,
> +					   "simple_ondemand",
> +					   &data->ondemand_data);
> +	if (IS_ERR(data->devfreq))
> +		return PTR_ERR(data->devfreq);
> +	devfreq_register_opp_notifier(dev, data->devfreq);

Use the devm_devfreq_register_opp_notifier().

> +
> +	data->dev = dev;
> +	platform_set_drvdata(pdev, data);
> +
> +	return 0;
> +}
> +
> +static int rk3399_dmcfreq_remove(struct platform_device *pdev)
> +{
> +	struct rk3399_dmcfreq *dmcfreq = platform_get_drvdata(pdev);
> +
> +	devfreq_remove_device(dmcfreq->devfreq);
> +	regulator_put(dmcfreq->vdd_center);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id rk3399dmc_devfreq_of_match[] = {
> +	{ .compatible = "rockchip,rk3399-dmc" },
> +	{ },
> +};
> +
> +static struct platform_driver rk3399_dmcfreq_driver = {
> +	.probe	= rk3399_dmcfreq_probe,
> +	.remove	= rk3399_dmcfreq_remove,
> +	.driver = {
> +		.name	= "rk3399-dmc-freq",
> +		.pm	= &rk3399_dmcfreq_pm,
> +		.of_match_table = rk3399dmc_devfreq_of_match,
> +	},
> +};
> +module_platform_driver(rk3399_dmcfreq_driver);
> +
> +MODULE_LICENSE("GPL v2");
> +MODULE_DESCRIPTION("RK3399 dmcfreq driver with devfreq framework");

You need to add the MODULE_AUTHOR information.

Regards,
Chanwoo Choi

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