Re: [PATCH v2 2/2] pwm:sunplus-pwm:Add Sunplus SoC PWM Driver

From: Uwe Kleine-König
Date: Fri Mar 04 2022 - 13:57:18 EST

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In reply to: Hammer Hsieh: "[PATCH v2 2/2] pwm:sunplus-pwm:Add Sunplus SoC PWM Driver"
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Hello,

On Fri, Mar 04, 2022 at 02:20:12PM +0800, Hammer Hsieh wrote:
> Add Sunplus SoC PWM Driver
>
> Signed-off-by: Hammer Hsieh <hammerh0314@xxxxxxxxx>
> ---
> Changes in v2:
> - Addressed all comments from Uwe Kleine-König.
> - rebase kernel to 5.17 rc5
>
> MAINTAINERS | 1 +
> drivers/pwm/Kconfig | 11 +++
> drivers/pwm/Makefile | 1 +
> drivers/pwm/pwm-sunplus.c | 229 ++++++++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 242 insertions(+)
> create mode 100644 drivers/pwm/pwm-sunplus.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 825b714..8710c8e 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -18535,6 +18535,7 @@ SUNPLUS PWM DRIVER
> M: Hammer Hsieh <hammerh0314@xxxxxxxxx>
> S: Maintained
> F: Documentation/devicetree/bindings/pwm/pwm-sunplus.yaml
> +F: drivers/pwm/pwm-sunplus.c
>
> SUNPLUS RTC DRIVER
> M: Vincent Shih <vincent.sunplus@xxxxxxxxx>
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index 21e3b05..54cfb50 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -572,6 +572,17 @@ config PWM_SUN4I
> To compile this driver as a module, choose M here: the module
> will be called pwm-sun4i.
>
> +config PWM_SUNPLUS
> + tristate "Sunplus PWM support"
> + depends on ARCH_SUNPLUS || COMPILE_TEST
> + depends on HAS_IOMEM && OF
> + help
> + Generic PWM framework driver for the PWM controller on
> + Sunplus SoCs.
> +
> + To compile this driver as a module, choose M here: the module
> + will be called pwm-sunplus.
> +
> config PWM_TEGRA
> tristate "NVIDIA Tegra PWM support"
> depends on ARCH_TEGRA || COMPILE_TEST
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index 708840b..be58616 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -53,6 +53,7 @@ obj-$(CONFIG_PWM_STM32) += pwm-stm32.o
> obj-$(CONFIG_PWM_STM32_LP) += pwm-stm32-lp.o
> obj-$(CONFIG_PWM_STMPE) += pwm-stmpe.o
> obj-$(CONFIG_PWM_SUN4I) += pwm-sun4i.o
> +obj-$(CONFIG_PWM_SUNPLUS) += pwm-sunplus.o
> obj-$(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-sunplus.c b/drivers/pwm/pwm-sunplus.c
> new file mode 100644
> index 0000000..170534f
> --- /dev/null
> +++ b/drivers/pwm/pwm-sunplus.c
> @@ -0,0 +1,229 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * PWM device driver for SUNPLUS SoCs

Is there a public manual available for this hardware? If yes, please add
a link here.

> + *
> + * Limitations:
> + * - Only supports normal polarity.

How does the HW behave when it's disabled? Usual candidates are:
- It freezes at where it currently is
- It outputs low
- It becomes tristate

Please note this in the Limitations section, too.

Another thing to mention is if running periods are completed when the
parameters change.

> + *
> + * Author: Hammer Hsieh <hammerh0314@xxxxxxxxx>
> + */
> +#include <linux/clk.h>
> +#include <linux/io.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +
> +#define PWM_SUP_CONTROL0 0x000
> +#define PWM_SUP_CONTROL1 0x004
> +#define PWM_SUP_FREQ_BASE 0x008
> +#define PWM_SUP_DUTY_BASE 0x018
> +#define PWM_SUP_FREQ(ch) (PWM_SUP_FREQ_BASE + 4 * (ch))
> +#define PWM_SUP_DUTY(ch) (PWM_SUP_DUTY_BASE + 4 * (ch))

I'd not give PWM_SUP_FREQ_BASE and PWM_SUP_DUTY_BASE a name here, just

#define PWM_SUP_FREQ(ch) (0x008 + 4 * (ch))
...

> +#define PWM_SUP_FREQ_MAX GENMASK(15, 0)
> +#define PWM_SUP_DUTY_MAX GENMASK(7, 0)
> +
> +#define PWM_SUP_NUM 4
> +#define PWM_BYPASS_BIT_SHIFT 8
> +#define PWM_DD_SEL_BIT_SHIFT 8
> +#define PWM_SUP_FREQ_SCALER 256

Please use a consistent prefix for the driver specific defines.

> +struct sunplus_pwm {
> + struct pwm_chip chip;
> + void __iomem *base;
> + struct clk *clk;
> + u32 approx_period[PWM_SUP_NUM];
> + u32 approx_duty_cycle[PWM_SUP_NUM];
> +};
> +
> +static inline struct sunplus_pwm *to_sunplus_pwm(struct pwm_chip *chip)
> +{
> + return container_of(chip, struct sunplus_pwm, chip);
> +}
> +
> +static void sunplus_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
> +{
> + struct sunplus_pwm *priv = to_sunplus_pwm(chip);
> + u32 value;
> +
> + /* disable pwm channel output */
> + value = readl(priv->base + PWM_SUP_CONTROL0);
> + value &= ~BIT(pwm->hwpwm);
> + writel(value, priv->base + PWM_SUP_CONTROL0);
> + /* disable pwm channel clk source */
> + value = readl(priv->base + PWM_SUP_CONTROL1);
> + value &= ~BIT(pwm->hwpwm);
> + writel(value, priv->base + PWM_SUP_CONTROL1);

the .free callback isn't supposed to modify the hardware.

> +}
> +
> +static int sunplus_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> + const struct pwm_state *state)
> +{
> + struct sunplus_pwm *priv = to_sunplus_pwm(chip);
> + u32 dd_freq, duty, value, value1;

As value and value1 hold register values for PWM_SUP_CONTROL0 and
PWM_SUP_CONTROL1, I'd call them control0 and control1 respectively.

> + u32 tmp, rate;
> + u64 max_period, period_ns, duty_ns, clk_rate;
> +
> + if (state->polarity != pwm->state.polarity)
> + return -EINVAL;
> +
> + if (!state->enabled) {
> + /* disable pwm channel output */
> + value = readl(priv->base + PWM_SUP_CONTROL0);
> + value &= ~BIT(pwm->hwpwm);

I'd give this one a name. Something like:

#define PWM_SUP_CONTROL_EN(ch) BIT(ch)

(Pick the right name from the manual.)

> + writel(value, priv->base + PWM_SUP_CONTROL0);
> + /* disable pwm channel clk source */
> + value = readl(priv->base + PWM_SUP_CONTROL1);
> + value &= ~BIT(pwm->hwpwm);
> + writel(value, priv->base + PWM_SUP_CONTROL1);
> + return 0;
> + }
> +
> + clk_rate = clk_get_rate(priv->clk);
> + rate = (u32)clk_rate / 100000;

This cast doesn't change anything, does it?

> + max_period = PWM_SUP_FREQ_MAX * (PWM_SUP_FREQ_SCALER * 10000 / rate);

Here you have rounding issues. Consider rate = 3329. Then you get
max_period = 0xffff * (2560000 / 3329) = 0xffff * 768 = 50330880.

However the actual result is 50396395.31...

Also dividing by the result of a division looses precision.

> +
> + if (state->period > max_period)
> + return -EINVAL;

No, you're supposed to implement the biggest period possible not bigger
than the requested period. So the right thing here is:

> + period_ns = state->period;

period = min(state->period, max_period);

> + duty_ns = state->duty_cycle;
> +
> + priv->approx_period[pwm->hwpwm] = (u32)period_ns / 100;
> + priv->approx_duty_cycle[pwm->hwpwm] = (u32)duty_ns / 100;

Tracking period_ns / 100 seems strange and vulnerable to rounding
issues.

> + /* cal pwm freq and check value under range */
> + dd_freq = rate * priv->approx_period[pwm->hwpwm] / (PWM_SUP_FREQ_SCALER * 100);

This is all too complicated, you just need:

dd_freq = mul_u64_u64_div_u64(clk_rate, period, (u64)PWM_SUP_FREQ_SCALER * NSEC_PER_SEC)

> + if (dd_freq == 0)
> + return -EINVAL;
> +
> + if (dd_freq > PWM_SUP_FREQ_MAX)
> + dd_freq = PWM_SUP_FREQ_MAX;
> +
> + writel(dd_freq, priv->base + PWM_SUP_FREQ(pwm->hwpwm));
> +
> + /* cal and set pwm duty */
> + value = readl(priv->base + PWM_SUP_CONTROL0);
> + value |= BIT(pwm->hwpwm);
> + value1 = readl(priv->base + PWM_SUP_CONTROL1);
> + value1 |= BIT(pwm->hwpwm);
> + if (duty_ns == period_ns) {
> + value |= BIT(pwm->hwpwm + PWM_BYPASS_BIT_SHIFT);
> + duty = PWM_SUP_DUTY_MAX;
> + } else {
> + value &= ~BIT(pwm->hwpwm + PWM_BYPASS_BIT_SHIFT);
> + tmp = priv->approx_duty_cycle[pwm->hwpwm] * PWM_SUP_FREQ_SCALER;
> + tmp /= priv->approx_period[pwm->hwpwm];

Please use the exact values available.

> + duty = (u32)tmp;
> + duty |= (pwm->hwpwm << PWM_DD_SEL_BIT_SHIFT);
> + }
> + writel(duty, priv->base + PWM_SUP_DUTY(pwm->hwpwm));
> + writel(value1, priv->base + PWM_SUP_CONTROL1);
> + writel(value, priv->base + PWM_SUP_CONTROL0);

What is the difference between CONTROL1 and CONTROL0?

> + return 0;
> +}
> +
> +static void sunplus_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> + struct pwm_state *state)
> +{
> + struct sunplus_pwm *priv = to_sunplus_pwm(chip);
> + u32 value, freq, duty, rate, freq_tmp, duty_tmp;
> + u64 tmp, clk_rate;
> +
> + value = readl(priv->base + PWM_SUP_CONTROL0);
> +
> + if (value & BIT(pwm->hwpwm)) {
> + clk_rate = clk_get_rate(priv->clk);
> + rate = (u32)clk_rate / 100000;
> + freq = readl(priv->base + PWM_SUP_FREQ(pwm->hwpwm));
> + duty = readl(priv->base + PWM_SUP_DUTY(pwm->hwpwm));
> + duty &= ~GENMASK(9, 8);
> +
> + freq_tmp = rate * priv->approx_period[pwm->hwpwm] / (PWM_SUP_FREQ_SCALER * 100);
> + duty_tmp = priv->approx_duty_cycle[pwm->hwpwm] * PWM_SUP_FREQ_SCALER /
> + priv->approx_period[pwm->hwpwm];
> +
> + if (freq == freq_tmp && duty == duty_tmp) {
> + state->period = priv->approx_period[pwm->hwpwm] * 100;
> + state->duty_cycle = priv->approx_duty_cycle[pwm->hwpwm] * 100;
> + } else {
> + tmp = (u64)freq * PWM_SUP_FREQ_SCALER * 10000;
> + state->period = div64_u64(tmp, rate);
> + tmp = (u64)freq * (u64)duty * 10000;
> + state->duty_cycle = div64_u64(tmp, rate);
> + }
> + state->enabled = true;
> + } else {
> + state->enabled = false;
> + }
> +
> + state->polarity = PWM_POLARITY_NORMAL;
> +}

When .get_state() is first called, .apply wasn't called yet. Then
priv->approx_period[pwm->hwpwm] is zero and the returned result is
wrong. Please read the register values and calculate the implemented
output without caching.

> +static const struct pwm_ops sunplus_pwm_ops = {
> + .free = sunplus_pwm_free,
> + .apply = sunplus_pwm_apply,
> + .get_state = sunplus_pwm_get_state,
> + .owner = THIS_MODULE,
> +};
> +
> +static int sunplus_pwm_probe(struct platform_device *pdev)
> +{
> + struct device *dev = &pdev->dev;
> + struct sunplus_pwm *priv;
> + int ret;
> +
> + priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> + if (!priv)
> + return -ENOMEM;
> +
> + priv->base = devm_platform_ioremap_resource(pdev, 0);
> + if (IS_ERR(priv->base))
> + return PTR_ERR(priv->base);
> +
> + priv->clk = devm_clk_get_optional(dev, NULL);
> + if (IS_ERR(priv->clk))
> + return dev_err_probe(dev, PTR_ERR(priv->clk),
> + "get pwm clock failed\n");

If priv->clk is the dummy clk, clk_get_rate returns 0. This is bad as
(at lease up to now) you divide by rate in .apply().

> +
> + ret = clk_prepare_enable(priv->clk);
> + if (ret)

missing error message

> + return ret;
> +
> + ret = devm_add_action_or_reset(dev,
> + (void(*)(void *))clk_disable_unprepare,

Without checking my C book I'm unsure if this is save on all platforms.
I'd implement a oneline function for this.

> + priv->clk);
> + if (ret)

missing error message

> + return ret;
> +
> + priv->chip.dev = dev;
> + priv->chip.ops = &sunplus_pwm_ops;
> + priv->chip.npwm = PWM_SUP_NUM;
> +
> + ret = devm_pwmchip_add(dev, &priv->chip);
> + if (ret < 0)
> + return dev_err_probe(dev, ret, "Cannot register sunplus PWM\n");
> +
> + return 0;
> +}
> +
> +static const struct of_device_id sunplus_pwm_of_match[] = {
> + { .compatible = "sunplus,sp7021-pwm", },
> + {}
> +};
> +MODULE_DEVICE_TABLE(of, sunplus_pwm_of_match);
> +
> +static struct platform_driver sunplus_pwm_driver = {
> + .probe = sunplus_pwm_probe,
> + .driver = {
> + .name = "sunplus-pwm",
> + .of_match_table = sunplus_pwm_of_match,
> + },
> +};
> +module_platform_driver(sunplus_pwm_driver);
> +
> +MODULE_DESCRIPTION("Sunplus SoC PWM Driver");
> +MODULE_AUTHOR("Hammer Hsieh <hammerh0314@xxxxxxxxx>");
> +MODULE_LICENSE("GPL");
> --
> 2.7.4
>
>

--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |

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