Re: [PATCH v4 4/6] PM / devfreq: Add dynamic scaling for imx8m ddr controller

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

On 11/12/19 2:23 AM, Leonard Crestez wrote:
> On 11.11.2019 05:18, Chanwoo Choi wrote:
>> Hi Leonard,
>>
>> On 11/9/19 7:39 AM, Leonard Crestez wrote:
>>> Add driver for dynamic scaling the DDR Controller on imx8m chips. Actual
>>> frequency switching is implemented inside TF-A, this driver wraps the
>>> SMC calls and synchronizes the clk tree.
>>>
>>> The DRAM clocks on imx8m have the following structure (abridged):
>>>
>>>   +----------+       |\            +------+
>>>   | dram_pll |-------|M| dram_core |      |
>>>   +----------+       |U|---------->| D    |
>>>                   /--|X|           |  D   |
>>>     dram_alt_root |  |/            |   R  |
>>>                   |                |    C |
>>>              +---------+           |      |
>>>              |FIX DIV/4|           |      |
>>>              +---------+           |      |
>>>    composite:     |                |      |
>>>   +----------+    |                |      |
>>>   | dram_alt |----/                |      |
>>>   +----------+                     |      |
>>>   | dram_apb |-------------------->|      |
>>>   +----------+                     +------+
>>>
>>> The dram_pll is used for higher rates and dram_alt is used for lower
>>> rates. The dram_alt and dram_apb clocks are "imx composite" and their
>>> parent can also be modified.
>>>
>>> This driver will prepare/enable the new parents ahead of switching (so
>>> that the expected roots are enabled) and afterwards it will call
>>> clk_set_parent to ensure the parents in clock framework are up-to-date.
>>>
>>> The driver relies on dram_pll dram_alt and dram_apb being marked with
>>> CLK_GET_RATE_NOCACHE for rate updates.
>>>
>>> Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
>>> ---
>>>   drivers/devfreq/Kconfig      |  10 +
>>>   drivers/devfreq/Makefile     |   1 +
>>>   drivers/devfreq/imx8m-ddrc.c | 416 +++++++++++++++++++++++++++++++++++
>>>   3 files changed, 427 insertions(+)
>>>   create mode 100644 drivers/devfreq/imx8m-ddrc.c
>>>
>>> diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
>>> index defe1d438710..c519fd27808f 100644
>>> --- a/drivers/devfreq/Kconfig
>>> +++ b/drivers/devfreq/Kconfig
>>> @@ -90,10 +90,20 @@ config ARM_EXYNOS_BUS_DEVFREQ
>>>   	  Each memory bus group could contain many memoby bus block. It reads
>>>   	  PPMU counters of memory controllers by using DEVFREQ-event device
>>>   	  and adjusts the operating frequencies and voltages with OPP support.
>>>   	  This does not yet operate with optimal voltages.
>>>   
>>> +config ARM_IMX8M_DDRC_DEVFREQ
>>> +	tristate "i.MX8M DDRC DEVFREQ Driver"
>>> +	depends on ARCH_MXC || COMPILE_TEST
>>> +	select DEVFREQ_GOV_SIMPLE_ONDEMAND
>>> +	select DEVFREQ_GOV_USERSPACE
>>> +	select PM_OPP
>>
>> It doesn't need to add. CONFIG_DEVFREQ add 'select PM_OPP'
>> because 'PM_OPP' is mandatory for devfreq.
> 
> OK.
> 
> All other drivers select PM_OPP, this was just copied
> 
>>> +	help
>>> +	  This adds the DEVFREQ driver for the i.MX8M DDR Controller. It allows
>>> +	  adjusting DRAM frequency.
>>> +
>>>   config ARM_TEGRA_DEVFREQ
>>>   	tristate "NVIDIA Tegra30/114/124/210 DEVFREQ Driver"
>>>   	depends on ARCH_TEGRA_3x_SOC || ARCH_TEGRA_114_SOC || \
>>>   		ARCH_TEGRA_132_SOC || ARCH_TEGRA_124_SOC || \
>>>   		ARCH_TEGRA_210_SOC || \
>>> diff --git a/drivers/devfreq/Makefile b/drivers/devfreq/Makefile
>>> index 338ae8440db6..3eb4d5e6635c 100644
>>> --- a/drivers/devfreq/Makefile
>>> +++ b/drivers/devfreq/Makefile
>>> @@ -7,10 +7,11 @@ 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
>>> +obj-$(CONFIG_ARM_IMX8M_DDRC_DEVFREQ)	+= imx8m-ddrc.o
>>>   obj-$(CONFIG_ARM_RK3399_DMC_DEVFREQ)	+= rk3399_dmc.o
>>>   obj-$(CONFIG_ARM_TEGRA_DEVFREQ)		+= tegra30-devfreq.o
>>>   obj-$(CONFIG_ARM_TEGRA20_DEVFREQ)	+= tegra20-devfreq.o
>>>   
>>>   # DEVFREQ Event Drivers
>>> diff --git a/drivers/devfreq/imx8m-ddrc.c b/drivers/devfreq/imx8m-ddrc.c
>>> new file mode 100644
>>> index 000000000000..51903fee21a7
>>> --- /dev/null
>>> +++ b/drivers/devfreq/imx8m-ddrc.c
>>> @@ -0,0 +1,416 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +/*
>>> + * Copyright 2019 NXP
>>> + */
>>> +
>>> +#include <linux/module.h>
>>> +#include <linux/device.h>
>>> +#include <linux/of_device.h>
>>> +#include <linux/platform_device.h>
>>> +#include <linux/devfreq.h>
>>> +#include <linux/pm_opp.h>
>>> +#include <linux/clk.h>
>>> +#include <linux/clk-provider.h>
>>> +#include <linux/arm-smccc.h>
>>> +
>>> +#define IMX_SIP_DDR_DVFS			0xc2000004
>>> +
>>> +/* Values starting from 0 switch to specific frequency */
>>> +#define IMX_SIP_DDR_FREQ_SET_HIGH		0x00
>>> +
>>> +/* Deprecated after moving IRQ handling to ATF */
>>> +#define IMX_SIP_DDR_DVFS_WAIT_CHANGE		0x0F
>>> +
>>> +/* Query available frequencies. */
>>> +#define IMX_SIP_DDR_DVFS_GET_FREQ_COUNT		0x10
>>> +#define IMX_SIP_DDR_DVFS_GET_FREQ_INFO		0x11
>>> +
>>> +/*
>>> + * This should be in a 1:1 mapping with devicetree OPPs but
>>> + * firmware provides additional info.
>>> + */
>>> +struct imx8m_ddrc_freq {
>>> +	unsigned long rate;
>>> +	unsigned long smcarg;
>>> +	int dram_core_parent_index;
>>> +	int dram_alt_parent_index;
>>> +	int dram_apb_parent_index;
>>> +};
>>> +
>>> +/* Hardware limitation */
>>> +#define IMX8M_DDRC_MAX_FREQ_COUNT 4
>>> +
>>> +/*
>>> + * i.MX8M DRAM Controller clocks have the following structure (abridged):
>>> + *
>>> + * +----------+       |\            +------+
>>> + * | dram_pll |-------|M| dram_core |      |
>>> + * +----------+       |U|---------->| D    |
>>> + *                 /--|X|           |  D   |
>>> + *   dram_alt_root |  |/            |   R  |
>>> + *                 |                |    C |
>>> + *            +---------+           |      |
>>> + *            |FIX DIV/4|           |      |
>>> + *            +---------+           |      |
>>> + *  composite:     |                |      |
>>> + * +----------+    |                |      |
>>> + * | dram_alt |----/                |      |
>>> + * +----------+                     |      |
>>> + * | dram_apb |-------------------->|      |
>>> + * +----------+                     +------+
>>> + *
>>> + * The dram_pll is used for higher rates and dram_alt is used for lower rates.
>>> + *
>>> + * Frequency switching is implemented in TF-A (via SMC call) and can change the
>>> + * configuration of the clocks, including mux parents. The dram_alt and
>>> + * dram_apb clocks are "imx composite" and their parent can change too.
>>> + *
>>> + * We need to prepare/enable the new mux parents head of switching and update
>>> + * their information afterwards.
>>> + */
>>> +struct imx8m_ddrc {
>>> +	struct devfreq_dev_profile profile;
>>> +	struct devfreq *devfreq;
>>> +
>>> +	/* For frequency switching: */
>>> +	struct clk *dram_core;
>>> +	struct clk *dram_pll;
>>> +	struct clk *dram_alt;
>>> +	struct clk *dram_apb;
>>> +
>>> +	int freq_count;
>>> +	struct imx8m_ddrc_freq freq_table[IMX8M_DDRC_MAX_FREQ_COUNT];
>>> +};
>>> +
>>> +static struct imx8m_ddrc_freq *imx8m_ddrc_find_freq(struct imx8m_ddrc *priv,
>>> +						    unsigned long rate)
>>> +{
>>> +	struct imx8m_ddrc_freq *freq;
>>> +	int i;
>>> +
>>> +	/*
>>> +	 * Firmware reports values in MT/s, so we round-down from Hz
>>> +	 * Rounding is extra generous to ensure a match.
>>> +	 */
>>> +	rate = DIV_ROUND_CLOSEST(rate, 250000);
>>> +	for (i = 0; i < priv->freq_count; ++i) {
>>> +		freq = &priv->freq_table[i];
>>> +		if (freq->rate == rate ||
>>> +				freq->rate + 1 == rate ||
>>> +				freq->rate - 1 == rate)
>>> +			return freq;
>>> +	}
>>> +
>>> +	return NULL;
>>> +}
>>> +
>>> +static void imx8m_ddrc_smc_set_freq(int target_freq)
>>> +{
>>> +	struct arm_smccc_res res;
>>> +	u32 online_cpus = 0;
>>> +	int cpu;
>>> +
>>> +	local_irq_disable();
>>
>> local_irq_disable is more proper than local_irq_save()?
> 
> There's no need to use save/restore because we know that irqs are 
> enabled when entering the function. This is only called from devfreq 
> set_target which runs in process context.

local_irq might affect the whole architecture and other running device driver
which requires the some CPU irq at the same time. Don't need to save the irqflag?

> 
>>
>>> +
>>> +	for_each_online_cpu(cpu)
>>> +		online_cpus |= (1 << (cpu * 8));
>>> +
>>> +	/* change the ddr freqency */
>>> +	arm_smccc_smc(IMX_SIP_DDR_DVFS, target_freq, online_cpus,
>>> +			0, 0, 0, 0, 0, &res);
>>> +
>>> +	local_irq_enable();
>>
>> ditto. local_irq_restore() instead of local_irq_enable()
>>
>>> +}
>>> +
>>> +struct clk *clk_get_parent_by_index(struct clk *clk, int index)
>>> +{
>>> +	struct clk_hw *hw;
>>> +
>>> +	hw = clk_hw_get_parent_by_index(__clk_get_hw(clk), index);
>>> +
>>> +	return hw ? hw->clk : NULL;
>>> +}
>>> +
>>> +static int imx8m_ddrc_set_freq(struct device *dev, struct imx8m_ddrc_freq *freq)
>>> +{
>>> +	struct imx8m_ddrc *priv = dev_get_drvdata(dev);
>>> +	struct clk *new_dram_core_parent;
>>> +	struct clk *new_dram_alt_parent;
>>> +	struct clk *new_dram_apb_parent;
>>> +	int ret;
>>> +
>>> +	new_dram_core_parent = clk_get_parent_by_index(
>>  > You can use 'clk_hw_get_parent_by_index' directly.
> 
> The helper above avoids duplicating ?:

I think that it is not duplicate. You use 'clk_hw_get_parent_by_index' function
and check the return value. it is essential behavior.

> 
>> And, you need to check whether the return value is NULL or not.
> Yes for dram_core_parent but others are deliberately allowed to be NULL. 
> For some setpoints some parents might be indifferent or require no 
> changes. For example when dram_core has pll as parent the expectation is 
> that dram_all will be OFF so parent is irrelevant.

If all case is not same as you commented, you just add the proper dev_warn
or dev_info message according to the h/w characteristic. Because user 
cannot know the detailed reason why don't check the return value.


> 
> Driver relies on the fact that clock API ignores prepare/enable for NULL 
> clocks. I can add a comment explaining that.
> 
>>> +			priv->dram_core, freq->dram_core_parent_index - 1);
>>> +	new_dram_alt_parent = clk_get_parent_by_index(
>>
>> ditto.
>>
>>> +			priv->dram_alt, freq->dram_alt_parent_index - 1);
>>> +	new_dram_apb_parent = clk_get_parent_by_index(
>>
>> ditto.
> 
>>> +			priv->dram_apb, freq->dram_apb_parent_index - 1);
>>> +
>>> +	/* increase reference counts and ensure clks are ON before switch */
>>> +	ret = clk_prepare_enable(new_dram_core_parent);
>>> +	if (ret) {
>>> +		dev_err(dev, "failed enable new dram_core parent: %d\n", ret);
>>> +		goto out;
>>> +	}
>>> +	ret = clk_prepare_enable(new_dram_alt_parent);
>>> +	if (ret) {
>>> +		dev_err(dev, "failed enable new dram_alt parent: %d\n", ret);
>>> +		goto out_dis_core;
>>
>> I think that 'dis' is not general expression for 'disable'.
>> Just, I think that 'out_disable_core' is better than 'out_dis_core'.
> 
> OK
> 
>>> +	}
>>> +	ret = clk_prepare_enable(new_dram_apb_parent);
>>> +	if (ret) {
>>> +		dev_err(dev, "failed enable new dram_apb parent: %d\n", ret);
>>> +		goto out_dis_alt;
>>
>> ditto.
>>
>>> +	}
>>> +
>>> +	imx8m_ddrc_smc_set_freq(freq->smcarg);
>>> +
>>> +	/* update parents in clk tree after switch. */
>>> +	ret = clk_set_parent(priv->dram_core, new_dram_core_parent);
>>> +	if (ret)
>>> +		dev_err(dev, "failed set dram_core parent: %d\n", ret);
>>
>> if you don't return directly, you better to use 'dev_warn' instead of 'dev_err'.
> 
> OK.
> 
>>> +	if (new_dram_alt_parent) {
>>> +		ret = clk_set_parent(priv->dram_alt, new_dram_alt_parent);
>>> +		if (ret)
>>> +			dev_err(dev, "failed set dram_alt parent: %d\n", ret);
>>
>> ditto. Use dev_warn.
>>   
>>> +	}
>>> +	if (new_dram_apb_parent) {
>>> +		ret = clk_set_parent(priv->dram_apb, new_dram_apb_parent);
>>> +		if (ret)
>>> +			dev_err(dev, "failed set dram_apb parent: %d\n", ret);
>>
>> ditto. Use dev_warn.
>>
>>> +	}
>>> +
>>> +	/*
>>> +	 * Explicitly refresh dram PLL rate.
>>> +	 *
>>> +	 * Even if it's marked with CLK_GET_RATE_NOCACHE the rate will not be
>>
>> nitpick:
>> What is more proper description either or 'Even if' or 'if' ?
> 
> Rate updates work for dram_alt/apb but not for dram_pll because 
> additional clocks might be present between the PLL and dram_core mux. 
> This happens *even if* pll is marked with CLK_GET_RATE_NOCACHE.

ok.

> 
>>> +	 * automatically refreshed when clk_get_rate is called on children.
>>> +	 */
>>> +	clk_get_rate(priv->dram_pll);
>>> +
>>> +	/*
>>> +	 * clk_set_parent transfer the reference count from old parent.
>>> +	 * now we drop extra reference counts used during the switch
>>> +	 */
>>> +	clk_disable_unprepare(new_dram_apb_parent);
>>> +out_dis_alt:
>>> +	clk_disable_unprepare(new_dram_alt_parent);
>>> +out_dis_core:
>>> +	clk_disable_unprepare(new_dram_core_parent);
>>> +out:
>>> +	return ret;
>>> +}
>>> +
>>> +static int imx8m_ddrc_target(struct device *dev, unsigned long *freq, u32 flags)
>>> +{
>>> +	struct imx8m_ddrc *priv = dev_get_drvdata(dev);
>>> +	struct imx8m_ddrc_freq *freq_info;
>>> +	struct dev_pm_opp *new_opp;
>>> +	unsigned long old_freq, new_freq;
>>> +	int ret;
>>> +
>>> +	new_opp = devfreq_recommended_opp(dev, freq, flags);
>>> +	if (IS_ERR(new_opp)) {
>>> +		ret = PTR_ERR(new_opp);
>>> +		dev_err(dev, "failed to get recommended opp: %d\n", ret);
>>> +		return ret;
>>> +	}
>>> +	dev_pm_opp_put(new_opp);
>>> +
>>> +	old_freq = clk_get_rate(priv->dram_core);
>>> +	if (*freq == old_freq)
>>> +		return 0;
>>> +
>>> +	freq_info = imx8m_ddrc_find_freq(priv, *freq);
>>> +	if (!freq_info)
>>> +		return -EINVAL;
>>> +	ret = imx8m_ddrc_set_freq(dev, freq_info);
>>
>> Need to check whether 'ret' is valid or not.
>>
>>> +
>>> +	/* Also read back the clk rate to verify switch was correct */
>>> +	new_freq = clk_get_rate(priv->dram_core);
>>> +	if (ret || *freq != new_freq)
>>
>> You should check 'ret' right after imx8m_ddrc_set_freq()
>> instead of this position.
> 
> OK, I can add two error paths.
> 
>>> +		dev_err(dev, "ddrc failed freq set to %lu from %lu, now at %lu\n",
>>> +			old_freq, *freq, new_freq);
>>> +	else
>>> +		dev_dbg(dev, "ddrc freq set to %lu (was %lu)\n",
>>> +			*freq, old_freq);
>>> +
>>> +	return ret;
>>> +}
>>> +
>>> +static int imx8m_ddrc_get_cur_freq(struct device *dev, unsigned long *freq)
>>> +{
>>> +	struct imx8m_ddrc *priv = dev_get_drvdata(dev);
>>> +
>>> +	*freq = clk_get_rate(priv->dram_core);
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +static int imx8m_ddrc_init_freq_info(struct device *dev)
>>> +{
>>> +	struct imx8m_ddrc *priv = dev_get_drvdata(dev);
>>> +	struct arm_smccc_res res;
>>> +	int index;
>>> +
>>> +	/*
>>> +	 * An error here means DDR DVFS API not supported by firmware
>>> +	 */
>>
>> Don't need to add multiple line comments. It is possible to be change as following:
>>
>> 	/* An error here means DDR DVFS API not supported by firmware */
> 
> OK.
>>> +	arm_smccc_smc(IMX_SIP_DDR_DVFS, IMX_SIP_DDR_DVFS_GET_FREQ_COUNT,
>>> +			0, 0, 0, 0, 0, 0, &res);
>>> +	priv->freq_count = res.a0;
>>> +	if (priv->freq_count <= 0 ||
>>> +			priv->freq_count > IMX8M_DDRC_MAX_FREQ_COUNT)
>>> +		return -ENODEV;
>>> +
>>> +	for (index = 0; index < priv->freq_count; ++index) {
>>> +		struct imx8m_ddrc_freq *freq = &priv->freq_table[index];
>>> +
>>> +		arm_smccc_smc(IMX_SIP_DDR_DVFS, IMX_SIP_DDR_DVFS_GET_FREQ_INFO,
>>> +				index, 0, 0, 0, 0, 0, &res);
>>> +		/* Result should be strictly positive */
>>> +		if ((long)res.a0 <= 0)
>>> +			return -ENODEV;
>>> +
>>> +		freq->rate = res.a0;
>>> +		freq->smcarg = index;
>>> +		freq->dram_core_parent_index = res.a1;
>>> +		freq->dram_alt_parent_index = res.a2;
>>> +		freq->dram_apb_parent_index = res.a3;
>>> +
>>> +		/* dram_core has 2 options: dram_pll or dram_alt_root */
>>> +		if (freq->dram_core_parent_index != 1 &&
>>> +				freq->dram_core_parent_index != 2)
>>> +			return -ENODEV;
>>> +		/* dram_apb and dram_alt have exactly 8 possible parents */
>>> +		if (freq->dram_alt_parent_index > 8 ||
>>> +				freq->dram_apb_parent_index > 8)
>>> +			return -ENODEV;
>>> +		/* dram_core from alt requires explicit dram_alt parent */
>>> +		if (freq->dram_core_parent_index == 2 &&
>>> +				freq->dram_alt_parent_index == 0)
>>> +			return -ENODEV;
>>> +	}
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +/* imx8m_ddrc_check_opps() - disable OPPs not supported by firmware */
>>
>> nitpick:
>> On this driver, there are no some description for internal function.
>> In order to keep the coding style, you better to move this comment
>> into function before 'freq = ULONG_MAX'.
> 
> Is it a problem if only some internal functions have documentation? I 
> can add docs to more functions.

It is not problem. It is just preferable way to add the comment.
Usually, if the function is public and exported, I added the detailed
function comment as following example of devfreq_add_device().

/**                                                                             
 656  * devfreq_add_device() - Add devfreq feature to the device                     
 657  * @dev:        the device to add devfreq feature.                              
 658  * @profile:    device-specific profile to run devfreq.                         
 659  * @governor_name:      name of the policy to choose frequency.                 
 660  * @data:       private data for the governor. The devfreq framework does not   
 661  *              touch this value.                                               
 662  */                                                                             
 663 struct devfreq *devfreq_add_device(struct device *dev,                          
 664                                    struct devfreq_dev_profile *profile,         
 665                                    const char *governor_name,                   
 666                                    void *data)              


Otherwise, if function is used in the only local with static keyword,
usually I don't add the above detailed description. Instead,
add the detailed comment into the function.

It is not the standard way. Just preferable way for the function description
if possible.



> 
> BTW: how can I generate devfreq documentation from these comments?
> 
>>> +static int imx8m_ddrc_check_opps(struct device *dev)
>>> +{
>>> +	struct imx8m_ddrc *priv = dev_get_drvdata(dev);
>>> +	struct imx8m_ddrc_freq *freq_info;
>>> +	struct dev_pm_opp *opp;
>>> +	unsigned long freq;
>>> +
>>> +	freq = ULONG_MAX;
>>> +	while (true) {
>>> +		opp = dev_pm_opp_find_freq_floor(dev, &freq);
>>> +		if (opp == ERR_PTR(-ERANGE))
>>> +			break;
>>> +		if (IS_ERR(opp)) {
>>> +			dev_err(dev, "Failed enumerating OPPs: %ld\n",
>>> +				PTR_ERR(opp));
>>> +			return PTR_ERR(opp);
>>> +		}
>>> +		dev_pm_opp_put(opp);
>>> +
>>> +		freq_info = imx8m_ddrc_find_freq(priv, freq);
>>> +		if (!freq_info) {
>>> +			dev_info(dev, "Disable unsupported OPP %luHz %luMT/s\n",
>>> +					freq, DIV_ROUND_CLOSEST(freq, 250000));
>>> +			dev_pm_opp_disable(dev, freq);
>>> +		}
>>> +
>>> +		freq--;
>>> +	}
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +static void imx8m_ddrc_exit(struct device *dev)
>>> +{
>>> +	dev_pm_opp_of_remove_table(dev);
>>> +}
>>> +
>>> +static int imx8m_ddrc_probe(struct platform_device *pdev)
>>> +{
>>> +	struct device *dev = &pdev->dev;
>>> +	struct imx8m_ddrc *priv;
>>> +	const char *gov = DEVFREQ_GOV_USERSPACE;
>>> +	int ret;
>>> +
>>> +	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
>>> +	if (!priv)
>>> +		return -ENOMEM;
>>> +
>>> +	platform_set_drvdata(pdev, priv);
>>> +
>>> +	ret = imx8m_ddrc_init_freq_info(dev);
>>> +	if (ret) {
>>> +		dev_err(dev, "failed to init firmware freq info: %d\n", ret);
>>> +		return ret;
>>> +	}
>>> +
>>> +	priv->dram_core = devm_clk_get(dev, "core");
>>> +	priv->dram_pll = devm_clk_get(dev, "pll");
>>> +	priv->dram_alt = devm_clk_get(dev, "alt");
>>> +	priv->dram_apb = devm_clk_get(dev, "apb");
>>> +	if (IS_ERR(priv->dram_core) ||
>>> +		IS_ERR(priv->dram_pll) ||
>>> +		IS_ERR(priv->dram_alt) ||
>>> +		IS_ERR(priv->dram_apb)) {
>>> +		ret = PTR_ERR(priv->devfreq);
>>> +		dev_err(dev, "failed to fetch clocks: %d\n", ret);
>>> +		return ret;
>>> +	}
>>> +
>>> +	ret = dev_pm_opp_of_add_table(dev);
>>> +	if (ret < 0) {
>>> +		dev_err(dev, "failed to get OPP table\n");
>>> +		return ret;
>>> +	}
>>> +
>>> +	ret = imx8m_ddrc_check_opps(dev);
>>> +	if (ret < 0)
>>> +		goto err;
>>> +
>>> +	priv->profile.polling_ms = 1000;
>>> +	priv->profile.target = imx8m_ddrc_target;
>>> +	priv->profile.exit = imx8m_ddrc_exit;
>>> +	priv->profile.get_cur_freq = imx8m_ddrc_get_cur_freq;
>>> +	priv->profile.initial_freq = clk_get_rate(priv->dram_core);
>>> +
>>> +	priv->devfreq = devm_devfreq_add_device(dev, &priv->profile,
>>> +						gov, NULL);
>>> +	if (IS_ERR(priv->devfreq)) {
>>> +		ret = PTR_ERR(priv->devfreq);
>>> +		dev_err(dev, "failed to add devfreq device: %d\n", ret);
>>> +		goto err;
>>> +	}
>>> +
>>> +	return 0;
>>> +
>>> +err:
>>> +	dev_pm_opp_of_remove_table(dev);
>>> +	return ret;
>>> +}
>>> +
>>> +static const struct of_device_id imx8m_ddrc_of_match[] = {
>>> +	{ .compatible = "fsl,imx8m-ddrc", },
>>> +	{ /* sentinel */ },
>>> +};
>>> +MODULE_DEVICE_TABLE(of, imx8m_ddrc_of_match);
>>> +
>>> +static struct platform_driver imx8m_ddrc_platdrv = {
>>> +	.probe		= imx8m_ddrc_probe,
>>> +	.driver = {
>>> +		.name	= "imx8m-ddrc-devfreq",
>>> +		.of_match_table = of_match_ptr(imx8m_ddrc_of_match),
>>> +	},
>>> +};
>>> +module_platform_driver(imx8m_ddrc_platdrv);
>>> +
>>> +MODULE_DESCRIPTION("i.MX8M DDR Controller frequency driver");
>>> +MODULE_AUTHOR("Leonard Crestez <leonard.crestez@nxp.com>");
>>> +MODULE_LICENSE("GPL v2");
> 
> 
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics