pwm: argon-fan-hat: Add Argon40 Fan HAT support

Add trivial PWM driver for Argon40 Fan HAT, which is a RaspberryPi
blower fan hat which can be controlled over I2C. Model this device
as a PWM, so the pwm-fan can be attached to it and handle thermal
zones and RPM management in a generic manner.

Signed-off-by: Marek Vasut <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Uwe Kleine-König <[e-mail]>

drivers/pwm/Kconfig

···
 	  To compile this driver as a module, choose M here: the module
 	  will be called pwm-apple.
 
+config PWM_ARGON_FAN_HAT
+	tristate "Argon40 Fan HAT support"
+	depends on I2C && OF
+	help
+	  Generic PWM framework driver for Argon40 Fan HAT.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called pwm-argon-fan-hat.
+
 config PWM_ATMEL
 	tristate "Atmel PWM support"
 	depends on ARCH_AT91 || COMPILE_TEST

drivers/pwm/Makefile

···
 obj-$(CONFIG_PWM_AB8500)	+= pwm-ab8500.o
 obj-$(CONFIG_PWM_ADP5585)	+= pwm-adp5585.o
 obj-$(CONFIG_PWM_APPLE)		+= pwm-apple.o
+obj-$(CONFIG_PWM_ARGON_FAN_HAT)	+= pwm-argon-fan-hat.o
 obj-$(CONFIG_PWM_ATMEL)		+= pwm-atmel.o
 obj-$(CONFIG_PWM_ATMEL_HLCDC_PWM)	+= pwm-atmel-hlcdc.o
 obj-$(CONFIG_PWM_ATMEL_TCB)	+= pwm-atmel-tcb.o

drivers/pwm/pwm-argon-fan-hat.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2025 Marek Vasut
+ *
+ * Limitations:
+ * - no support for offset/polarity
+ * - fixed 30 kHz period
+ *
+ * Argon Fan HAT https://argon40.com/products/argon-fan-hat
+ */
+
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+#include <linux/pwm.h>
+
+#define ARGON40_FAN_HAT_PERIOD_NS	33333	/* ~30 kHz */
+
+#define ARGON40_FAN_HAT_REG_DUTY_CYCLE	0x80
+
+static int argon_fan_hat_round_waveform_tohw(struct pwm_chip *chip,
+					     struct pwm_device *pwm,
+					     const struct pwm_waveform *wf,
+					     void *_wfhw)
+{
+	u8 *wfhw = _wfhw;
+
+	if (wf->duty_length_ns > ARGON40_FAN_HAT_PERIOD_NS)
+		*wfhw = 100;
+	else
+		*wfhw = mul_u64_u64_div_u64(wf->duty_length_ns, 100, ARGON40_FAN_HAT_PERIOD_NS);
+
+	return 0;
+}
+
+static int argon_fan_hat_round_waveform_fromhw(struct pwm_chip *chip,
+					       struct pwm_device *pwm,
+					       const void *_wfhw,
+					       struct pwm_waveform *wf)
+{
+	const u8 *wfhw = _wfhw;
+
+	wf->period_length_ns = ARGON40_FAN_HAT_PERIOD_NS;
+	wf->duty_length_ns = DIV64_U64_ROUND_UP(wf->period_length_ns * *wfhw, 100);
+	wf->duty_offset_ns = 0;
+
+	return 0;
+}
+
+static int argon_fan_hat_write_waveform(struct pwm_chip *chip,
+					struct pwm_device *pwm,
+					const void *_wfhw)
+{
+	struct i2c_client *i2c = pwmchip_get_drvdata(chip);
+	const u8 *wfhw = _wfhw;
+
+	return i2c_smbus_write_byte_data(i2c, ARGON40_FAN_HAT_REG_DUTY_CYCLE, *wfhw);
+}
+
+static const struct pwm_ops argon_fan_hat_pwm_ops = {
+	.sizeof_wfhw = sizeof(u8),
+	.round_waveform_fromhw = argon_fan_hat_round_waveform_fromhw,
+	.round_waveform_tohw = argon_fan_hat_round_waveform_tohw,
+	.write_waveform = argon_fan_hat_write_waveform,
+	/*
+	 * The controller does not provide any way to read info back,
+	 * reading from the controller stops the fan, therefore there
+	 * is no .read_waveform here.
+	 */
+};
+
+static int argon_fan_hat_i2c_probe(struct i2c_client *i2c)
+{
+	struct pwm_chip *chip = devm_pwmchip_alloc(&i2c->dev, 1, 0);
+	int ret;
+
+	if (IS_ERR(chip))
+		return PTR_ERR(chip);
+
+	chip->ops = &argon_fan_hat_pwm_ops;
+	pwmchip_set_drvdata(chip, i2c);
+
+	ret = devm_pwmchip_add(&i2c->dev, chip);
+	if (ret)
+		return dev_err_probe(&i2c->dev, ret, "Could not add PWM chip\n");
+
+	return 0;
+}
+
+static const struct of_device_id argon_fan_hat_dt_ids[] = {
+	{ .compatible = "argon40,fan-hat" },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, argon_fan_hat_dt_ids);
+
+static struct i2c_driver argon_fan_hat_driver = {
+	.driver = {
+		.name = "argon-fan-hat",
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+		.of_match_table = argon_fan_hat_dt_ids,
+	},
+	.probe = argon_fan_hat_i2c_probe,
+};
+
+module_i2c_driver(argon_fan_hat_driver);
+
+MODULE_AUTHOR("Marek Vasut <[e-mail]>");
+MODULE_DESCRIPTION("Argon40 Fan HAT");
+MODULE_LICENSE("GPL");