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SubjectRe: [RFC 2/4] pwm: sifive: Add a driver for SiFive SoC PWM
On Tue, Oct 09, 2018 at 11:51:23AM -0700, Atish Patra wrote:
> From: "Wesley W. Terpstra" <wesley@sifive.com>
>
> Adds a PWM driver for PWM chip present in SiFive's HiFive Unleashed SoC.
>
> Signed-off-by: Wesley W. Terpstra <wesley@sifive.com>
> [Atish: Various fixes and code cleanup]
> Signed-off-by: Atish Patra <atish.patra@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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