Re: [PATCH RFC v6 2/9] PM / devfreq: Add generic imx bus scaling driver

[Leonard Crestez <leonard.crestez@nxp.com>]

On 16.12.2019 03:00, Chanwoo Choi wrote:
> Hi,
> 
> Also, I think that 'devfreq' word is not proper for device driver name.
> imx-bus.c or imx-noc.c or others to inform the role of this driver of developer.

I'll rename to "imx-bus". Calling it "imx-noc" is not appropriate 
because I also want to use it for PL301 NICs.

> And, I have a question.
> This driver adds the devfreq device with either passive governor
> or userspace governor.
> 
> As I understood, the devfreq device with passive governor
> will be operated with imx8m-ddrc.c driver.
> But, when is operating with userspace governor?

There are multiple scalable buses inside the SOC, for example there's a 
NIC for display controllers and one for (pci+usb). They can use 
userspace governor for explicit frequency control.

> I think that you better to add the explanation to description
> for two scenarios how to operate with interconnect provider
> on either passive governor or userspace governor usage case.

I'll elaborate the example in bindings.

> On 12/13/19 10:51 AM, Chanwoo Choi wrote:
>> On 12/13/19 10:30 AM, Chanwoo Choi wrote:
>>> Hi,
>>>
>>> On 11/15/19 5:09 AM, Leonard Crestez wrote:
>>>> Add initial support for dynamic frequency switching on pieces of the imx
>>>> interconnect fabric.
>>>>
>>>> All this driver does is set a clk rate based on an opp table, it does
>>>> not map register areas.
>>>>
>>>> Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
>>>> ---
>>>>   drivers/devfreq/Kconfig       |   9 ++
>>>>   drivers/devfreq/Makefile      |   1 +
>>>>   drivers/devfreq/imx-devfreq.c | 150 ++++++++++++++++++++++++++++++++++
>>>>   3 files changed, 160 insertions(+)
>>>>   create mode 100644 drivers/devfreq/imx-devfreq.c
>>>>
>>>> diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
>>>> index 923a6132e741..fef5ce831e90 100644
>>>> --- a/drivers/devfreq/Kconfig
>>>> +++ b/drivers/devfreq/Kconfig
>>>> @@ -98,10 +98,19 @@ config ARM_IMX8M_DDRC_DEVFREQ
>>>>   	select DEVFREQ_GOV_USERSPACE
>>>>   	help
>>>>   	  This adds the DEVFREQ driver for the i.MX8M DDR Controller. It allows
>>>>   	  adjusting DRAM frequency.
>>>>   
>>>> +config ARM_IMX_DEVFREQ
>>>> +	tristate "i.MX Generic DEVFREQ Driver"
>>>> +	depends on ARCH_MXC || COMPILE_TEST
>>>> +	select DEVFREQ_GOV_PASSIVE
>>>> +	select DEVFREQ_GOV_USERSPACE
>>>> +	help
>>>> +	  This adds the generic DEVFREQ driver for i.MX interconnects. It
>>>> +	  allows adjusting NIC/NOC 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 3eb4d5e6635c..61d0edee16f7 100644
>>>> --- a/drivers/devfreq/Makefile
>>>> +++ b/drivers/devfreq/Makefile
>>>> @@ -8,10 +8,11 @@ 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-$(CONFIG_ARM_IMX_DEVFREQ)		+= imx-devfreq.o
>>>>   obj-$(CONFIG_ARM_RK3399_DMC_DEVFREQ)	+= rk3399_dmc.o
>>>>   obj-$(CONFIG_ARM_TEGRA_DEVFREQ)		+= tegra30-devfreq.o
>>>>   obj-$(CONFIG_ARM_TEGRA20_DEVFREQ)	+= tegra20-devfreq.o
>>>>   
>>>>   # DEVFREQ Event Drivers
>>>> diff --git a/drivers/devfreq/imx-devfreq.c b/drivers/devfreq/imx-devfreq.c
>>>> new file mode 100644
>>>> index 000000000000..620b344e87aa
>>>> --- /dev/null
>>>> +++ b/drivers/devfreq/imx-devfreq.c
>>>> @@ -0,0 +1,150 @@
>>>> +// SPDX-License-Identifier: GPL-2.0
>>>> +/*
>>>> + * Copyright 2019 NXP
>>>> + */
>>>> +
>>>> +#include <linux/clk.h>
>>>> +#include <linux/devfreq.h>
>>>> +#include <linux/device.h>
>>>> +#include <linux/module.h>
>>>> +#include <linux/of_device.h>
>>>> +#include <linux/pm_opp.h>
>>>> +#include <linux/platform_device.h>
>>>> +#include <linux/slab.h>
>>>> +
>>>> +struct imx_devfreq {
>>>> +	struct devfreq_dev_profile profile;
>>>> +	struct devfreq *devfreq;
>>>> +	struct clk *clk;
>>>> +	struct devfreq_passive_data passive_data;
>>>> +};
>>>> +
>>>> +static int imx_devfreq_target(struct device *dev,
>>>> +			      unsigned long *freq, u32 flags)
>>>
>>> Don't use space for the indentation. Please use only tab.

OK

>>>> +{
>>>> +	struct imx_devfreq *priv = dev_get_drvdata(dev);
>>>> +	struct dev_pm_opp *new_opp;
>>>> +	unsigned long 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;
>>>> +	}
>>>> +	new_freq = dev_pm_opp_get_freq(new_opp);
>>>> +	dev_pm_opp_put(new_opp);
>>>> +
>>>> +	return clk_set_rate(priv->clk, new_freq);
>>>> +}
>>>> +
>>>> +static int imx_devfreq_get_cur_freq(struct device *dev, unsigned long *freq)
>>>> +{
>>>> +	struct imx_devfreq *priv = dev_get_drvdata(dev);
>>>> +
>>>> +	*freq = clk_get_rate(priv->clk);
>>>> +
>>>> +	return 0;
>>>> +}
>>>> +
>>>> +static int imx_devfreq_get_dev_status(struct device *dev,
>>>> +				      struct devfreq_dev_status *stat)
>>>
>>> ditto. Please use tab for the indentation.
>>>
>>>> +{
>>>> +	struct imx_devfreq *priv = dev_get_drvdata(dev);
>>>> +
>>>> +	stat->busy_time = 0;
>>>> +	stat->total_time = 0;
>>>> +	stat->current_frequency = clk_get_rate(priv->clk);
>>>> +
>>>> +	return 0;
>>>> +}
>>>> +
>>>> +static void imx_devfreq_exit(struct device *dev)
>>>> +{
>>>> +	dev_pm_opp_of_remove_table(dev);
>>>> +}
>>>> +
>>>> +static int imx_devfreq_probe(struct platform_device *pdev)
>>>> +{
>>>> +	struct device *dev = &pdev->dev;
>>>> +	struct imx_devfreq *priv;
>>>
>>> How about changing the variable name 'priv' to 'imx' or 'imx_data'?
>>> because it is not easy to catch the role of 'priv' from variable name.

The name "priv" refers to private data of current device: it is short 
and not ambiguous in this context. I don't think that mentioning "imx" 
adds any additional useful information.

It doesn't seem like there's much of a convention for "local variable 
containing private data", for example exynos-bus.c uses "struct 
exynos_bus* bus" internally.

>>>
>>>> +	const char *gov = DEVFREQ_GOV_USERSPACE;
>>>> +	void *govdata = NULL;
>>>
>>> How about changing the variable name 'govdata' to 'gov_data'?
>>> - govdata -> gov_data

OK

>>>> +	int ret;
>>>> +
>>>> +	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
>>>> +	if (!priv)
>>>> +		return -ENOMEM;
>>>> +
>>>> +	priv->clk = devm_clk_get(dev, NULL);
>>>
>>> nitpick: because the clock-name is not mandatory.
>>> Don't need to specify the clock name to inform the role of clock
>>> of other developer/user?
>>>
>>> For example, "ddr", "bus" and so on.

I'll call this bus, but I'm not sure it's useful when a single clock is 
involved.

>> And, this driver doesn't include the 'clk_prepare_enable'.
>> how to enable the clock?

Clocks are either always on or perhaps controlled by some other 
peripheral. This driver only provides scaling.

>>>> +	if (IS_ERR(priv->clk)) {
>>>> +		ret = PTR_ERR(priv->clk);
>>>> +		dev_err(dev, "failed to fetch clk: %d\n", ret);
>>>> +		return ret;
>>>> +	}
>>>> +	platform_set_drvdata(pdev, priv);
>>>> +
>>>> +	ret = dev_pm_opp_of_add_table(dev);
>>>> +	if (ret < 0) {
>>>> +		dev_err(dev, "failed to get OPP table\n");
>>>> +		return ret;
>>>> +	}
>>>> +
>>>> +	priv->profile.polling_ms = 1000;
>>>> +	priv->profile.target = imx_devfreq_target;
>>>> +	priv->profile.get_dev_status = imx_devfreq_get_dev_status;
>>>> +	priv->profile.exit = imx_devfreq_exit;
>>>> +	priv->profile.get_cur_freq = imx_devfreq_get_cur_freq;
>>>> +	priv->profile.initial_freq = clk_get_rate(priv->clk);
>>>> +
>>>> +	/* Handle passive devfreq parent link */
>>>> +	priv->passive_data.parent = devfreq_get_devfreq_by_phandle(dev, 0);
>>>> +	if (!IS_ERR(priv->passive_data.parent)) {
>>>> +		dev_info(dev, "setup passive link to %s\n",
>>>> +			 dev_name(priv->passive_data.parent->dev.parent));
>>>> +		gov = DEVFREQ_GOV_PASSIVE;
>>>> +		govdata = &priv->passive_data;
>>>> +	} else if (priv->passive_data.parent != ERR_PTR(-ENODEV)) {
>>>> +		// -ENODEV means no parent: not an error.
>>>> +		ret = PTR_ERR(priv->passive_data.parent);
>>>> +		if (ret != -EPROBE_DEFER)
>>>> +			dev_warn(dev, "failed to get initialize passive parent: %d\n",
>>>> +				 ret);
>>>> +		goto err;
>>>> +	}
>>>
>>> You better to change the exception handling as following: It is more simple.
>>>
>>> 	} else if (PTR_ERR(priv->passive_data.parent) == -EPROBE_DEFER)
>>> 			|| PTR_ERR(priv->passive_data.parent) == -ENODEV) {
>>> 		goto err;
>>> 	} else {
>>> 		ret = PTR_ERR(priv->passive_data.parent);
>>> 		dev_err(dev, "failed to get initialize passive parent: %d\n", ret);
>>> 		goto err;
>>> 	}

But -ENODEV is not an error, it means no passive parent was found.

>>>> +	priv->devfreq = devm_devfreq_add_device(dev, &priv->profile,
>>>> +						gov, govdata);
>>>> +	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 imx_devfreq_of_match[] = {
>>>> +	{ .compatible = "fsl,imx8m-noc", },
>>>> +	{ .compatible = "fsl,imx8m-nic", },
>>>> +	{ /* sentinel */ },
>>>> +};
>>>> +MODULE_DEVICE_TABLE(of, imx_devfreq_of_match);
>>>> +
>>>> +static struct platform_driver imx_devfreq_platdrv = {
>>>> +	.probe		= imx_devfreq_probe,
>>>> +	.driver = {
>>>> +		.name	= "imx-devfreq",
>>>> +		.of_match_table = of_match_ptr(imx_devfreq_of_match),
>>>> +	},
>>>> +};
>>>> +module_platform_driver(imx_devfreq_platdrv);
>>>> +
>>>> +MODULE_DESCRIPTION("Generic i.MX bus frequency driver");
>>>
>>> If this driver is for bus frequency, you better to use 'bus' for the clock-name
>>> for the readability.

OK