linux-kernel - Re: [PATCH v4 03/10] pwm: max7360: Add MAX7360 PWM support

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Message-ID: <e7epeegrp6cz27s63gnqe7b6me7h3rn5d6mo7mbd6rwgnwyys6@j7f6cy4uy3wq>
Date: Thu, 13 Mar 2025 22:03:27 +0100
From: Uwe Kleine-König <ukleinek@...nel.org>
To: mathieu.dubois-briand@...tlin.com, 
	Linus Walleij <linus.walleij@...aro.org>
Cc: Lee Jones <lee@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Kamel Bouhara <kamel.bouhara@...tlin.com>, Bartosz Golaszewski <brgl@...ev.pl>, 
	Dmitry Torokhov <dmitry.torokhov@...il.com>, Michael Walle <mwalle@...nel.org>, 
	Mark Brown <broonie@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Danilo Krummrich <dakr@...nel.org>, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org, linux-input@...r.kernel.org, 
	linux-pwm@...r.kernel.org, andriy.shevchenko@...el.com, 
	Grégory Clement <gregory.clement@...tlin.com>, Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v4 03/10] pwm: max7360: Add MAX7360 PWM support

Hello Mathieu,

On Fri, Feb 14, 2025 at 12:49:53PM +0100, mathieu.dubois-briand@...tlin.com wrote:
> diff --git a/drivers/pwm/pwm-max7360.c b/drivers/pwm/pwm-max7360.c
> new file mode 100644
> index 000000000000..f1257c20add2
> --- /dev/null
> +++ b/drivers/pwm/pwm-max7360.c
> @@ -0,0 +1,213 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright 2024 Bootlin
> + *
> + * Author: Kamel BOUHARA <kamel.bouhara@...tlin.com>
> + * Author: Mathieu Dubois-Briand <mathieu.dubois-briand@...tlin.com>
> + *
> + * Limitations:
> + * - Only supports normal polarity.
> + * - The period is fixed to 2 ms.
> + * - Only the duty cycle can be changed, new values are applied at the beginning
> + *   of the next cycle.
> + * - When disabled, the output is put in Hi-Z.
> + */
> +#include <linux/err.h>
> +#include <linux/math.h>
> +#include <linux/mfd/max7360.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +#include <linux/regmap.h>
> +
> +#define MAX7360_NUM_PWMS			8
> +#define MAX7360_PWM_MAX_RES			255
> +#define MAX7360_PWM_PERIOD_NS			2000000 /* 500 Hz */
> +#define MAX7360_PWM_COMMON_PWN			BIT(5)
> +#define MAX7360_PWM_CTRL_ENABLE(n)		BIT(n)
> +#define MAX7360_PWM_PORT(n)			BIT(n)
> +
> +struct max7360_pwm {
> +	struct device *parent;
> +	struct regmap *regmap;
> +};
> +
> +struct max7360_pwm_waveform {
> +	u8 duty_steps;
> +};
> +
> +static inline struct max7360_pwm *max7360_pwm_from_chip(struct pwm_chip *chip)
> +{
> +	return pwmchip_get_drvdata(chip);
> +}
> +
> +static int max7360_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm)
> +{
> +	struct max7360_pwm *max7360_pwm;
> +	int ret;
> +
> +	max7360_pwm = max7360_pwm_from_chip(chip);
> +	ret = max7360_port_pin_request(max7360_pwm->parent, pwm->hwpwm, true);
> +	if (ret) {
> +		dev_warn(&chip->dev, "failed to request pwm-%d\n", pwm->hwpwm);

Please drop this warning, just returning ret here is fine. (The rule of
thumb is: Emit runtime messages only in probe, not during usage.)

> +		return ret;
> +	}
> +
> +	ret = regmap_write_bits(max7360_pwm->regmap,
> +				MAX7360_REG_PWMCFG(pwm->hwpwm),
> +				MAX7360_PWM_COMMON_PWN,
> +				0);
> +	if (ret)
> +		return ret;
> +
> +	return regmap_write_bits(max7360_pwm->regmap, MAX7360_REG_PORTS,
> +				 MAX7360_PWM_PORT(pwm->hwpwm),
> +				 MAX7360_PWM_PORT(pwm->hwpwm));
> +}
> +
> +static void max7360_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
> +{
> +	struct max7360_pwm *max7360_pwm;
> +
> +	max7360_pwm = max7360_pwm_from_chip(chip);
> +	max7360_port_pin_request(max7360_pwm->parent, pwm->hwpwm, false);

Would be nice if pinmuxing would be abstracted as a pinctrl driver. Not
sure how much effort that is. Maybe Linus has an idea?

> +}
> +
> [...]
> +
> +static int max7360_pwm_write_waveform(struct pwm_chip *chip,
> +				      struct pwm_device *pwm,
> +				      const void *_wfhw)
> +{
> +	const struct max7360_pwm_waveform *wfhw = _wfhw;
> +	struct max7360_pwm *max7360_pwm;
> +	unsigned int val;
> +	int ret;
> +
> +	max7360_pwm = max7360_pwm_from_chip(chip);
> +
> +	val = (wfhw->duty_steps == 0) ? 0 : MAX7360_PWM_CTRL_ENABLE(pwm->hwpwm);

Does not setting MAX7360_PWM_CTRL_ENABLE result in the pin going to
Hi-Z? If yes: That's wrong. You're only supposed to do that if
period_length_ns = 0 was requested. If no: This needs a comment why
duty_steps = 0 is special here.

> +	ret = regmap_write_bits(max7360_pwm->regmap, MAX7360_REG_GPIOCTRL,
> +				MAX7360_PWM_CTRL_ENABLE(pwm->hwpwm), val);
> +
> +	if (!ret && wfhw->duty_steps != 0) {
> +		ret = regmap_write(max7360_pwm->regmap, MAX7360_REG_PWM(pwm->hwpwm),
> +				   wfhw->duty_steps);
> +	}
> +
> +	return ret;
> +}
> +
> +static int max7360_pwm_read_waveform(struct pwm_chip *chip,
> +				     struct pwm_device *pwm,
> +				     void *_wfhw)
> +{
> +	struct max7360_pwm_waveform *wfhw = _wfhw;
> +	struct max7360_pwm *max7360_pwm;
> +	unsigned int val;
> +	int ret;
> +
> +	max7360_pwm = max7360_pwm_from_chip(chip);
> +
> +	ret = regmap_read(max7360_pwm->regmap, MAX7360_REG_GPIOCTRL, &val);
> +	if (ret)
> +		return ret;
> +
> +	if (val & MAX7360_PWM_CTRL_ENABLE(pwm->hwpwm)) {
> +		ret = regmap_read(max7360_pwm->regmap, MAX7360_REG_PWM(pwm->hwpwm),
> +				  &val);
> +		val = wfhw->duty_steps;

wfhw->duty_steps = val;

> +	} else {
> +		wfhw->duty_steps = 0;
> +	}
> +
> +	return ret;
> +}

Best regards
Uwe

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