[RFC 2/4] pwm: sifive: Add a driver for SiFive SoC PWM

Thierry Reding thierry.reding at gmail.com
Wed Oct 10 07:13:41 PDT 2018


On Tue, Oct 09, 2018 at 11:51:23AM -0700, Atish Patra wrote:
> From: "Wesley W. Terpstra" <wesley at sifive.com>
> 
> Adds a PWM driver for PWM chip present in SiFive's HiFive Unleashed SoC.
> 
> Signed-off-by: Wesley W. Terpstra <wesley at sifive.com>
> [Atish: Various fixes and code cleanup]
> Signed-off-by: Atish Patra <atish.patra at wdc.com>
> ---
>  drivers/pwm/Kconfig      |  10 ++
>  drivers/pwm/Makefile     |   1 +
>  drivers/pwm/pwm-sifive.c | 240 +++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 251 insertions(+)
>  create mode 100644 drivers/pwm/pwm-sifive.c
> 
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index 504d2527..dd12144d 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -378,6 +378,16 @@ config PWM_SAMSUNG
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called pwm-samsung.
>  
> +config PWM_SIFIVE
> +	tristate "SiFive PWM support"
> +	depends on OF
> +	depends on COMMON_CLK
> +	help
> +	  Generic PWM framework driver for SiFive SoCs.
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called pwm-sifive.
> +
>  config PWM_SPEAR
>  	tristate "STMicroelectronics SPEAr PWM support"
>  	depends on PLAT_SPEAR
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index 9c676a0d..30089ca6 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -37,6 +37,7 @@ obj-$(CONFIG_PWM_RCAR)		+= pwm-rcar.o
>  obj-$(CONFIG_PWM_RENESAS_TPU)	+= pwm-renesas-tpu.o
>  obj-$(CONFIG_PWM_ROCKCHIP)	+= pwm-rockchip.o
>  obj-$(CONFIG_PWM_SAMSUNG)	+= pwm-samsung.o
> +obj-$(CONFIG_PWM_SIFIVE)	+= pwm-sifive.o
>  obj-$(CONFIG_PWM_SPEAR)		+= pwm-spear.o
>  obj-$(CONFIG_PWM_STI)		+= pwm-sti.o
>  obj-$(CONFIG_PWM_STM32)		+= pwm-stm32.o
> diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c
> new file mode 100644
> index 00000000..99580025
> --- /dev/null
> +++ b/drivers/pwm/pwm-sifive.c
> @@ -0,0 +1,240 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2017 SiFive
> + */
> +#include <dt-bindings/pwm/pwm.h>

What do you need this for? Your driver should only be dealing with enum
pwm_polarity, not the defines from the above header. This works but only
because PWM_POLARITY_INVERTED and PWM_POLARITY_INVERSED happen to be the
same value.

> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +#include <linux/slab.h>
> +#include <linux/clk.h>
> +#include <linux/io.h>

Keep these in alphabetical order, please.

> +
> +#define MAX_PWM			4
> +
> +/* Register offsets */
> +#define REG_PWMCFG		0x0
> +#define REG_PWMCOUNT		0x8
> +#define REG_PWMS		0x10
> +#define	REG_PWMCMP0		0x20
> +
> +/* PWMCFG fields */
> +#define BIT_PWM_SCALE		0
> +#define BIT_PWM_STICKY		8
> +#define BIT_PWM_ZERO_ZMP	9
> +#define BIT_PWM_DEGLITCH	10
> +#define BIT_PWM_EN_ALWAYS	12
> +#define BIT_PWM_EN_ONCE		13
> +#define BIT_PWM0_CENTER		16
> +#define BIT_PWM0_GANG		24
> +#define BIT_PWM0_IP		28
> +
> +#define SIZE_PWMCMP		4
> +#define MASK_PWM_SCALE		0xf
> +
> +struct sifive_pwm_device {
> +	struct pwm_chip		chip;
> +	struct notifier_block	notifier;
> +	struct clk		*clk;
> +	void __iomem		*regs;
> +	unsigned int		approx_period;
> +	unsigned int		real_period;
> +};

No need to align these. A single space is enough to separate variable
type and name.

> +
> +static inline struct sifive_pwm_device *to_sifive_pwm_chip(struct pwm_chip *c)
> +{
> +	return container_of(c, struct sifive_pwm_device, chip);
> +}
> +
> +static int sifive_pwm_apply(struct pwm_chip *chip, struct pwm_device *dev,
> +			    struct pwm_state *state)
> +{
> +	struct sifive_pwm_device *pwm = to_sifive_pwm_chip(chip);
> +	unsigned int duty_cycle;
> +	u32 frac;
> +
> +	duty_cycle = state->duty_cycle;
> +	if (!state->enabled)
> +		duty_cycle = 0;
> +	if (state->polarity == PWM_POLARITY_NORMAL)
> +		duty_cycle = state->period - duty_cycle;

That's not actually polarity inversion. This is "lightweight" inversion
which should be up to the consumer, not the PWM driver, to implement. If
you don't actually have a knob in hardware to switch the polarity, don't
support it.

> +
> +	frac = ((u64)duty_cycle << 16) / state->period;
> +	frac = min(frac, 0xFFFFU);
> +
> +	iowrite32(frac, pwm->regs + REG_PWMCMP0 + (dev->hwpwm * SIZE_PWMCMP));

writel()?

> +
> +	if (state->enabled) {
> +		state->period = pwm->real_period;
> +		state->duty_cycle = ((u64)frac * pwm->real_period) >> 16;
> +		if (state->polarity == PWM_POLARITY_NORMAL)
> +			state->duty_cycle = state->period - state->duty_cycle;
> +	}
> +
> +	return 0;
> +}
> +
> +static void sifive_pwm_get_state(struct pwm_chip *chip, struct pwm_device *dev,
> +				 struct pwm_state *state)
> +{
> +	struct sifive_pwm_device *pwm = to_sifive_pwm_chip(chip);
> +	unsigned long duty;
> +
> +	duty = ioread32(pwm->regs + REG_PWMCMP0 + (dev->hwpwm * SIZE_PWMCMP));

readl()? Maybe also change duty to u32, which is what readl() returns.

> +
> +	state->period     = pwm->real_period;
> +	state->duty_cycle = ((u64)duty * pwm->real_period) >> 16;
> +	state->polarity   = PWM_POLARITY_INVERSED;
> +	state->enabled    = duty > 0;
> +}
> +
> +static const struct pwm_ops sifive_pwm_ops = {
> +	.get_state	= sifive_pwm_get_state,
> +	.apply		= sifive_pwm_apply,
> +	.owner		= THIS_MODULE,

Again, no need to artificially align these.

> +};
> +
> +static struct pwm_device *sifive_pwm_xlate(struct pwm_chip *chip,
> +					   const struct of_phandle_args *args)
> +{
> +	struct sifive_pwm_device *pwm = to_sifive_pwm_chip(chip);
> +	struct pwm_device *dev;
> +
> +	if (args->args[0] >= chip->npwm)
> +		return ERR_PTR(-EINVAL);
> +
> +	dev = pwm_request_from_chip(chip, args->args[0], NULL);
> +	if (IS_ERR(dev))
> +		return dev;
> +
> +	/* The period cannot be changed on a per-PWM basis */
> +	dev->args.period   = pwm->real_period;
> +	dev->args.polarity = PWM_POLARITY_NORMAL;
> +	if (args->args[1] & PWM_POLARITY_INVERTED)
> +		dev->args.polarity = PWM_POLARITY_INVERSED;
> +
> +	return dev;
> +}
> +
> +static void sifive_pwm_update_clock(struct sifive_pwm_device *pwm,
> +				    unsigned long rate)
> +{
> +	/* (1 << (16+scale)) * 10^9/rate = real_period */
> +	unsigned long scalePow = (pwm->approx_period * (u64)rate) / 1000000000;
> +	int scale = ilog2(scalePow) - 16;
> +
> +	scale = clamp(scale, 0, 0xf);
> +	iowrite32((1 << BIT_PWM_EN_ALWAYS) | (scale << BIT_PWM_SCALE),
> +		  pwm->regs + REG_PWMCFG);
> +
> +	pwm->real_period = (1000000000ULL << (16 + scale)) / rate;
> +}
> +
> +static int sifive_pwm_clock_notifier(struct notifier_block *nb,
> +				     unsigned long event, void *data)
> +{
> +	struct clk_notifier_data *ndata = data;
> +	struct sifive_pwm_device *pwm = container_of(nb,
> +						     struct sifive_pwm_device,
> +						     notifier);
> +
> +	if (event == POST_RATE_CHANGE)
> +		sifive_pwm_update_clock(pwm, ndata->new_rate);
> +
> +	return NOTIFY_OK;
> +}

Does this mean that the PWM source clock can be shared with other IP
blocks? What happens if some other user sets a frequency that we can't
support? Or what if the clock rate change results in a real period that
is out of the limits that are considered valid?

> +static int sifive_pwm_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct device_node *node = pdev->dev.of_node;
> +	struct sifive_pwm_device *pwm;
> +	struct pwm_chip *chip;
> +	struct resource *res;
> +	int ret;
> +
> +	pwm = devm_kzalloc(dev, sizeof(*pwm), GFP_KERNEL);
> +	if (!pwm)
> +		return -ENOMEM;
> +
> +	chip = &pwm->chip;
> +	chip->dev = dev;
> +	chip->ops = &sifive_pwm_ops;
> +	chip->of_xlate = sifive_pwm_xlate;
> +	chip->of_pwm_n_cells = 2;
> +	chip->base = -1;
> +
> +	ret = of_property_read_u32(node, "sifive,npwm", &chip->npwm);
> +	if (ret < 0 || chip->npwm > MAX_PWM)
> +		chip->npwm = MAX_PWM;

This property is not documented. Also, why is it necessary? Do you
expect the number of PWMs to differ depending on the instance of the IP
block? I would argue that the number of PWMs can be derived from the
compatible string, so it's unnecessary here.

I think you can also remove the MAX_PWM macro, since that's only used in
one location and it's meaning is very clear in the context, so the
symbolic name isn't useful.

> +
> +	ret = of_property_read_u32(node, "sifive,approx-period",
> +				   &pwm->approx_period);
> +	if (ret < 0) {
> +		dev_err(dev, "Unable to read sifive,approx-period from DTS\n");
> +		return -ENOENT;
> +	}

Maybe propagate ret instead of always returning -ENOENT?

> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	pwm->regs = devm_ioremap_resource(dev, res);
> +	if (IS_ERR(pwm->regs)) {
> +		dev_err(dev, "Unable to map IO resources\n");
> +		return PTR_ERR(pwm->regs);
> +	}
> +
> +	pwm->clk = devm_clk_get(dev, NULL);
> +	if (IS_ERR(pwm->clk)) {
> +		dev_err(dev, "Unable to find controller clock\n");
> +		return PTR_ERR(pwm->clk);
> +	}
> +
> +	/* Watch for changes to underlying clock frequency */
> +	pwm->notifier.notifier_call = sifive_pwm_clock_notifier;
> +	clk_notifier_register(pwm->clk, &pwm->notifier);

Check for errors from this?

> +
> +	/* Initialize PWM config */
> +	sifive_pwm_update_clock(pwm, clk_get_rate(pwm->clk));
> +
> +	/* No interrupt handler needed yet */

That's not a useful comment.

> +
> +	ret = pwmchip_add(chip);
> +	if (ret < 0) {
> +		dev_err(dev, "cannot register PWM: %d\n", ret);
> +		clk_notifier_unregister(pwm->clk, &pwm->notifier);

Might be worth introducing a managed version of clk_notifier_register()
so that we can avoid having to unregister it.

> +		return ret;
> +	}
> +
> +	platform_set_drvdata(pdev, pwm);
> +	dev_info(dev, "SiFive PWM chip registered %d PWMs\n", chip->npwm);

Remove this, or at least make it dev_dbg(). This is not noteworthy news,
so no need to bother the user with it.

> +
> +	return 0;
> +}
> +
> +static int sifive_pwm_remove(struct platform_device *dev)
> +{
> +	struct sifive_pwm_device *pwm = platform_get_drvdata(dev);
> +	struct pwm_chip *chip = &pwm->chip;

Not sure that this intermediate variable is useful, might as well use
&pwm->chip in the one location where you need it.

> +
> +	clk_notifier_unregister(pwm->clk, &pwm->notifier);
> +	return pwmchip_remove(chip);
> +}
> +
> +static const struct of_device_id sifive_pwm_of_match[] = {
> +	{ .compatible = "sifive,pwm0" },
> +	{ .compatible = "sifive,fu540-c000-pwm0" },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, sifive_pwm_of_match);
> +
> +static struct platform_driver sifive_pwm_driver = {
> +	.probe = sifive_pwm_probe,
> +	.remove = sifive_pwm_remove,
> +	.driver = {
> +		.name = "pwm-sifivem",

Why does this have the 'm' at the end? I don't see that anywhere else in
the names.

> +		.of_match_table = of_match_ptr(sifive_pwm_of_match),

No need for of_match_ptr() here since you depend on OF, so this is
always going to expand to sifive_pwm_of_match.

Thierry
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