[PATCHv8,1/2] pwm: Add Allwinner SoC support

This adds a generic PWM framework driver for the PWM controller
found on Allwinner SoCs.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 drivers/pwm/Kconfig     |   9 ++
 drivers/pwm/Makefile    |   1 +
 drivers/pwm/pwm-sun4i.c | 371 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 381 insertions(+)
 create mode 100644 drivers/pwm/pwm-sun4i.c

Hello Alexandre,

On 19.10.2014 21:28, Alexandre Belloni wrote:
> This adds a generic PWM framework driver for the PWM controller
> found on Allwinner SoCs.
> 
> Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
> Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
>  drivers/pwm/Kconfig     |   9 ++
>  drivers/pwm/Makefile    |   1 +
>  drivers/pwm/pwm-sun4i.c | 371 ++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 381 insertions(+)
>  create mode 100644 drivers/pwm/pwm-sun4i.c
> 
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index 3865dfb9ed08..424359d3cbb1 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -262,6 +262,15 @@ config PWM_STI
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called pwm-sti.
>  
> +config PWM_SUN4I
> +	tristate "Allwinner sun4i PWM support"
> +	depends on ARCH_SUNXI || COMPILE_TEST
> +	help
> +	  Generic PWM framework driver for Allwinner sun4i and sun7i SoCs.
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called pwm-sun4i.
> +
>  config PWM_TEGRA
>  	tristate "NVIDIA Tegra PWM support"
>  	depends on ARCH_TEGRA
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index c458606c3755..d607804deea1 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -24,6 +24,7 @@ obj-$(CONFIG_PWM_ROCKCHIP)	+= pwm-rockchip.o
>  obj-$(CONFIG_PWM_SAMSUNG)	+= pwm-samsung.o
>  obj-$(CONFIG_PWM_SPEAR)		+= pwm-spear.o
>  obj-$(CONFIG_PWM_STI)		+= pwm-sti.o
> +obj-$(CONFIG_PWM_SUN4I)		+= pwm-sun4i.o
>  obj-$(CONFIG_PWM_TEGRA)		+= pwm-tegra.o
>  obj-$(CONFIG_PWM_TIECAP)	+= pwm-tiecap.o
>  obj-$(CONFIG_PWM_TIEHRPWM)	+= pwm-tiehrpwm.o
> diff --git a/drivers/pwm/pwm-sun4i.c b/drivers/pwm/pwm-sun4i.c
> new file mode 100644
> index 000000000000..918f8ee79b51
> --- /dev/null
> +++ b/drivers/pwm/pwm-sun4i.c
> @@ -0,0 +1,371 @@
> +/*
> + * Driver for Allwinner sun4i Pulse Width Modulation Controller
> + *
> + * Copyright (C) 2014 Alexandre Belloni <alexandre.belloni@free-electrons.com>
> + *
> + * Licensed under GPLv2.
> + */
> +
> +#include <linux/bitops.h>
> +#include <linux/clk.h>
> +#include <linux/err.h>
> +#include <linux/io.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +#include <linux/slab.h>
> +#include <linux/time.h>
> +
> +#define PWM_CTRL_REG		0x0
> +
> +#define PWM_CH_PRD_BASE		0x4
> +#define PWM_CH_PRD_OFFSET	0x4
> +#define PWM_CH_PRD(ch)		(PWM_CH_PRD_BASE + PWM_CH_PRD_OFFSET * (ch))
> +
> +#define PWMCH_OFFSET		15
> +#define PWM_PRESCAL_MASK	GENMASK(3, 0)
> +#define PWM_PRESCAL_OFF		0
> +#define PWM_EN			BIT(4)
> +#define PWM_ACT_STATE		BIT(5)
> +#define PWM_CLK_GATING		BIT(6)
> +#define PWM_MODE		BIT(7)
> +#define PWM_PULSE		BIT(8)
> +#define PWM_BYPASS		BIT(9)
> +
> +#define PWM_RDY_BASE		28
> +#define PWM_RDY_OFFSET		1
> +#define PWM_RDY(ch)		BIT(PWM_RDY_BASE + PWM_RDY_OFFSET * (ch))
> +
> +#define PWM_PRD(prd)		(((prd) - 1) << 16)
> +#define PWM_PRD_MASK		GENMASK(15, 0)
> +
> +#define PWM_DTY_MASK		GENMASK(15, 0)
> +
> +#define BIT_CH(bit, chan)	((bit) << ((chan) * PWMCH_OFFSET))
> +
> +static const u32 prescaler_table[] = {
> +	120,
> +	180,
> +	240,
> +	360,
> +	480,
> +	0,
> +	0,
> +	0,
> +	12000,
> +	24000,
> +	36000,
> +	48000,
> +	72000,
> +	0,
> +	0,
> +	0, /* Actually 1 but tested separately */
> +};
> +
> +struct sun4i_pwm_data {
> +	bool has_prescaler_bypass;
> +	bool has_rdy;
> +};
> +
> +struct sun4i_pwm_chip {
> +	struct pwm_chip chip;
> +	struct clk *clk;
> +	void __iomem *base;
> +	struct mutex ctrl_lock;

why do you use mutex? I haven't found any blocking subcalls under
protection, a spinlock seems to fit better here.

Vladimir

> +	const struct sun4i_pwm_data *data;
> +};
> +
> +static inline struct sun4i_pwm_chip *to_sun4i_pwm_chip(struct pwm_chip *chip)
> +{
> +	return container_of(chip, struct sun4i_pwm_chip, chip);
> +}
> +
> +static inline u32 sun4i_pwm_readl(struct sun4i_pwm_chip *chip,
> +				  unsigned long offset)
> +{
> +	return readl(chip->base + offset);
> +}
> +
> +static inline void sun4i_pwm_writel(struct sun4i_pwm_chip *chip,
> +				    u32 val, unsigned long offset)
> +{
> +	writel(val, chip->base + offset);
> +}
> +
> +static int sun4i_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> +			    int duty_ns, int period_ns)
> +{
> +	struct sun4i_pwm_chip *sun4i_pwm = to_sun4i_pwm_chip(chip);
> +	u32 clk_rate, prd, dty, val, clk_gate;
> +	u64 div = 0;
> +	unsigned int prescaler = 0;
> +	int err;
> +
> +	clk_rate = clk_get_rate(sun4i_pwm->clk);
> +
> +	if (sun4i_pwm->data->has_prescaler_bypass) {
> +		/* First, test without any prescaler when available */
> +		prescaler = PWM_PRESCAL_MASK;
> +		/*
> +		 * When not using any prescaler, the clock period in nanoseconds
> +		 * is not an integer so round it half up instead of
> +		 * truncating to get less surprising values.
> +		 */
> +		div = clk_rate * (u64)period_ns + NSEC_PER_SEC/2;
> +		do_div(div, NSEC_PER_SEC);
> +		if (div - 1 > PWM_PRD_MASK)
> +			prescaler = 0;
> +	}
> +
> +	if (prescaler == 0) {
> +		/* Go up from the first divider */
> +		for (prescaler = 0; prescaler < PWM_PRESCAL_MASK; prescaler++) {
> +			if (!prescaler_table[prescaler])
> +				continue;
> +			div = clk_rate / prescaler_table[prescaler];
> +			div = div * (u64)period_ns;
> +			do_div(div, NSEC_PER_SEC);
> +			if (div - 1 <= PWM_PRD_MASK)
> +				break;
> +		}
> +
> +		if (div - 1 > PWM_PRD_MASK) {
> +			dev_err(chip->dev, "period exceeds the maximum value\n");
> +			return -EINVAL;
> +		}
> +	}
> +
> +	prd = div;
> +	div *= duty_ns;
> +	do_div(div, period_ns);
> +	dty = div;
> +
> +	err = clk_prepare_enable(sun4i_pwm->clk);
> +	if (err) {
> +		dev_err(chip->dev, "failed to enable PWM clock\n");
> +		return err;
> +	}
> +
> +	mutex_lock(&sun4i_pwm->ctrl_lock);
> +	val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
> +
> +	if (sun4i_pwm->data->has_rdy && (val & PWM_RDY(pwm->hwpwm))) {
> +		mutex_unlock(&sun4i_pwm->ctrl_lock);
> +		clk_disable_unprepare(sun4i_pwm->clk);
> +		return -EBUSY;
> +	}
> +
> +	clk_gate = val & BIT_CH(PWM_CLK_GATING, pwm->hwpwm);
> +	if (clk_gate) {
> +		val &= ~BIT_CH(PWM_CLK_GATING, pwm->hwpwm);
> +		sun4i_pwm_writel(sun4i_pwm, val, PWM_CTRL_REG);
> +	}
> +
> +	val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
> +	val &= ~BIT_CH(PWM_PRESCAL_MASK, pwm->hwpwm);
> +	val |= BIT_CH(prescaler, pwm->hwpwm);
> +	sun4i_pwm_writel(sun4i_pwm, val, PWM_CTRL_REG);
> +
> +	val = (dty & PWM_DTY_MASK) | PWM_PRD(prd);
> +	sun4i_pwm_writel(sun4i_pwm, val, PWM_CH_PRD(pwm->hwpwm));
> +
> +	if (clk_gate) {
> +		val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
> +		val |= clk_gate;
> +		sun4i_pwm_writel(sun4i_pwm, val, PWM_CTRL_REG);
> +	}
> +
> +	mutex_unlock(&sun4i_pwm->ctrl_lock);
> +	clk_disable_unprepare(sun4i_pwm->clk);
> +
> +	return 0;
> +}
> +
> +static int sun4i_pwm_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm,
> +				  enum pwm_polarity polarity)
> +{
> +	struct sun4i_pwm_chip *sun4i_pwm = to_sun4i_pwm_chip(chip);
> +	u32 val;
> +	int ret;
> +
> +	ret = clk_prepare_enable(sun4i_pwm->clk);
> +	if (ret) {
> +		dev_err(chip->dev, "failed to enable PWM clock\n");
> +		return ret;
> +	}
> +
> +	mutex_lock(&sun4i_pwm->ctrl_lock);
> +	val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
> +
> +	if (polarity != PWM_POLARITY_NORMAL)
> +		val &= ~BIT_CH(PWM_ACT_STATE, pwm->hwpwm);
> +	else
> +		val |= BIT_CH(PWM_ACT_STATE, pwm->hwpwm);
> +
> +	sun4i_pwm_writel(sun4i_pwm, val, PWM_CTRL_REG);
> +
> +	mutex_unlock(&sun4i_pwm->ctrl_lock);
> +	clk_disable_unprepare(sun4i_pwm->clk);
> +
> +	return 0;
> +}
> +
> +static int sun4i_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> +{
> +	struct sun4i_pwm_chip *sun4i_pwm = to_sun4i_pwm_chip(chip);
> +	u32 val;
> +	int ret;
> +
> +	ret = clk_prepare_enable(sun4i_pwm->clk);
> +	if (ret) {
> +		dev_err(chip->dev, "failed to enable PWM clock\n");
> +		return ret;
> +	}
> +
> +	mutex_lock(&sun4i_pwm->ctrl_lock);
> +	val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
> +	val |= BIT_CH(PWM_EN, pwm->hwpwm);
> +	val |= BIT_CH(PWM_CLK_GATING, pwm->hwpwm);
> +	sun4i_pwm_writel(sun4i_pwm, val, PWM_CTRL_REG);
> +	mutex_unlock(&sun4i_pwm->ctrl_lock);
> +
> +	return 0;
> +}
> +
> +static void sun4i_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> +{
> +	struct sun4i_pwm_chip *sun4i_pwm = to_sun4i_pwm_chip(chip);
> +	u32 val;
> +
> +	mutex_lock(&sun4i_pwm->ctrl_lock);
> +	val = sun4i_pwm_readl(sun4i_pwm, PWM_CTRL_REG);
> +	val &= ~BIT_CH(PWM_EN, pwm->hwpwm);
> +	val &= ~BIT_CH(PWM_CLK_GATING, pwm->hwpwm);
> +	sun4i_pwm_writel(sun4i_pwm, val, PWM_CTRL_REG);
> +	mutex_unlock(&sun4i_pwm->ctrl_lock);
> +
> +	clk_disable_unprepare(sun4i_pwm->clk);
> +}
> +
> +static const struct pwm_ops sun4i_pwm_ops = {
> +	.config = sun4i_pwm_config,
> +	.set_polarity = sun4i_pwm_set_polarity,
> +	.enable = sun4i_pwm_enable,
> +	.disable = sun4i_pwm_disable,
> +	.owner = THIS_MODULE,
> +};
> +
> +static const struct sun4i_pwm_data sun4i_pwm_data_a10 = {
> +	.has_prescaler_bypass = false,
> +	.has_rdy = false,
> +};
> +
> +static const struct sun4i_pwm_data sun4i_pwm_data_a20 = {
> +	.has_prescaler_bypass = true,
> +	.has_rdy = true,
> +};
> +
> +static const struct of_device_id sun4i_pwm_dt_ids[] = {
> +	{
> +		.compatible = "allwinner,sun4i-a10-pwm",
> +		.data = &sun4i_pwm_data_a10,
> +	}, {
> +		.compatible = "allwinner,sun7i-a20-pwm",
> +		.data = &sun4i_pwm_data_a20,
> +	}, {
> +		/* sentinel */
> +	},
> +};
> +MODULE_DEVICE_TABLE(of, sun4i_pwm_dt_ids);
> +
> +static int sun4i_pwm_probe(struct platform_device *pdev)
> +{
> +	struct sun4i_pwm_chip *pwm;
> +	struct resource *res;
> +	u32 val;
> +	int i, ret;
> +	const struct of_device_id *match;
> +
> +	match = of_match_device(sun4i_pwm_dt_ids, &pdev->dev);
> +
> +	pwm = devm_kzalloc(&pdev->dev, sizeof(*pwm), GFP_KERNEL);
> +	if (!pwm)
> +		return -ENOMEM;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	pwm->base = devm_ioremap_resource(&pdev->dev, res);
> +	if (IS_ERR(pwm->base))
> +		return PTR_ERR(pwm->base);
> +
> +	pwm->clk = devm_clk_get(&pdev->dev, NULL);
> +	if (IS_ERR(pwm->clk))
> +		return PTR_ERR(pwm->clk);
> +
> +	pwm->chip.dev = &pdev->dev;
> +	pwm->chip.ops = &sun4i_pwm_ops;
> +	pwm->chip.base = -1;
> +	pwm->chip.npwm = 2;
> +	pwm->chip.can_sleep = true;
> +	pwm->chip.of_xlate = of_pwm_xlate_with_flags;
> +	pwm->chip.of_pwm_n_cells = 3;
> +	pwm->data = match->data;
> +
> +	mutex_init(&pwm->ctrl_lock);
> +
> +	ret = pwmchip_add(&pwm->chip);
> +	if (ret < 0) {
> +		dev_err(&pdev->dev, "failed to add PWM chip: %d\n", ret);
> +		goto error;
> +	}
> +
> +	platform_set_drvdata(pdev, pwm);
> +
> +	ret = clk_prepare_enable(pwm->clk);
> +	if (ret) {
> +		dev_err(&pdev->dev, "failed to enable PWM clock\n");
> +		goto clk_error;
> +	}
> +
> +	val = sun4i_pwm_readl(pwm, PWM_CTRL_REG);
> +	for (i = 0; i < pwm->chip.npwm; i++) {
> +		if (!(val & BIT_CH(PWM_ACT_STATE, i)))
> +			pwm->chip.pwms[i].polarity = PWM_POLARITY_INVERSED;
> +	}
> +	clk_disable_unprepare(pwm->clk);
> +
> +	return 0;
> +
> +clk_error:
> +	pwmchip_remove(&pwm->chip);
> +
> +error:
> +	mutex_destroy(&pwm->ctrl_lock);
> +	return ret;
> +}
> +
> +static int sun4i_pwm_remove(struct platform_device *pdev)
> +{
> +	struct sun4i_pwm_chip *pwm = platform_get_drvdata(pdev);
> +
> +	mutex_destroy(&pwm->ctrl_lock);
> +
> +	return pwmchip_remove(&pwm->chip);
> +}
> +
> +static struct platform_driver sun4i_pwm_driver = {
> +	.driver = {
> +		.name = "sun4i-pwm",
> +		.of_match_table = sun4i_pwm_dt_ids,
> +	},
> +	.probe = sun4i_pwm_probe,
> +	.remove = sun4i_pwm_remove,
> +};
> +module_platform_driver(sun4i_pwm_driver);
> +
> +MODULE_ALIAS("platform:sun4i-pwm");
> +MODULE_AUTHOR("Alexandre Belloni <alexandre.belloni@free-electrons.com>");
> +MODULE_DESCRIPTION("Allwinner sun4i PWM driver");
> +MODULE_LICENSE("GPL v2");
> 
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Hi,

On 20/10/2014 at 00:22:57 +0300, Vladimir Zapolskiy wrote :
> > +struct sun4i_pwm_chip {
> > +	struct pwm_chip chip;
> > +	struct clk *clk;
> > +	void __iomem *base;
> > +	struct mutex ctrl_lock;
> 
> why do you use mutex? I haven't found any blocking subcalls under
> protection, a spinlock seems to fit better here.
> 

A mutex here will do the right thing. The lock is never taken in
interrupt context and a mutex is spinning for a few cycles before
putting the thread to sleep. I'm not sure why you feel a spinlock would
be better here.

Hi Alexandre,

On 20.10.2014 13:29, Alexandre Belloni wrote:
> Hi,
> 
> On 20/10/2014 at 00:22:57 +0300, Vladimir Zapolskiy wrote :
>>> +struct sun4i_pwm_chip {
>>> +	struct pwm_chip chip;
>>> +	struct clk *clk;
>>> +	void __iomem *base;
>>> +	struct mutex ctrl_lock;
>>
>> why do you use mutex? I haven't found any blocking subcalls under
>> protection, a spinlock seems to fit better here.
>>
> 
> A mutex here will do the right thing. The lock is never taken in
> interrupt context and a mutex is spinning for a few cycles before
> putting the thread to sleep.

and why do you want to put a thread to sleep in context of the driver?

> I'm not sure why you feel a spinlock would be better here.
> 

Only because a spinlock is lighter than a mutex.

With best wishes,
Vladimir
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On 20/10/2014 at 16:10:31 +0300, Vladimir Zapolskiy wrote :
> Hi Alexandre,
> 
> On 20.10.2014 13:29, Alexandre Belloni wrote:
> > Hi,
> > 
> > On 20/10/2014 at 00:22:57 +0300, Vladimir Zapolskiy wrote :
> >>> +struct sun4i_pwm_chip {
> >>> +	struct pwm_chip chip;
> >>> +	struct clk *clk;
> >>> +	void __iomem *base;
> >>> +	struct mutex ctrl_lock;
> >>
> >> why do you use mutex? I haven't found any blocking subcalls under
> >> protection, a spinlock seems to fit better here.
> >>
> > 
> > A mutex here will do the right thing. The lock is never taken in
> > interrupt context and a mutex is spinning for a few cycles before
> > putting the thread to sleep.
> 
> and why do you want to put a thread to sleep in context of the driver?
> 

Because the PWM is getting configured from either a kernel thread or a
userspace thread accessing /sys. So you probably want the current thread
to sleep so the other thread accessing the register can finish. Unless
you are on smp and then, the mutex will spin for some time and your
other cpu will be finished by then.

On Mon, Oct 20, 2014 at 07:06:04PM +0200, Alexandre Belloni wrote:
> Because the PWM is getting configured from either a kernel thread or a
> userspace thread accessing /sys. So you probably want the current thread
> to sleep so the other thread accessing the register can finish. Unless
> you are on smp and then, the mutex will spin for some time and your
> other cpu will be finished by then.

I agree with Vladimir.  A spinlock would be better here.  You're only
needing to sleep for a short time (the time it takes to complete the
register accesses) and to have a competing thread go through a context
switch twice is stupidly expensive compared to having it wait a short
time for the spinlock to be released.

What the driver could do with is using the relaxed IO accessors too,
if you care about eliminating the unnecessary barriers in there.

On 20.10.2014 20:06, Alexandre Belloni wrote:
> On 20/10/2014 at 16:10:31 +0300, Vladimir Zapolskiy wrote :
>> Hi Alexandre,
>>
>> On 20.10.2014 13:29, Alexandre Belloni wrote:
>>> Hi,
>>>
>>> On 20/10/2014 at 00:22:57 +0300, Vladimir Zapolskiy wrote :
>>>>> +struct sun4i_pwm_chip {
>>>>> +	struct pwm_chip chip;
>>>>> +	struct clk *clk;
>>>>> +	void __iomem *base;
>>>>> +	struct mutex ctrl_lock;
>>>>
>>>> why do you use mutex? I haven't found any blocking subcalls under
>>>> protection, a spinlock seems to fit better here.
>>>>
>>>
>>> A mutex here will do the right thing. The lock is never taken in
>>> interrupt context and a mutex is spinning for a few cycles before
>>> putting the thread to sleep.
>>
>> and why do you want to put a thread to sleep in context of the driver?
>>
> 
> Because the PWM is getting configured from either a kernel thread or a
> userspace thread accessing /sys. So you probably want the current thread
> to sleep so the other thread accessing the register can finish. Unless
> you are on smp and then, the mutex will spin for some time and your
> other cpu will be finished by then.
> 

You answer why a thread sleeps, if you use a mutex in the driver. But
you don't answer my question why do you want to put a thread to sleep.

As for me you introduce the excessive heaviness for no reason. There is
no need to sleep while waiting for completion of a register writing.

With best wishes,
Vladimir
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