[PATCH v5 3/3] pwm: argon-fan-hat: Add Argon40 Fan HAT support

[Marek Vasut <marek.vasut+renesas@mailbox.org>]

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 <marek.vasut+renesas@mailbox.org>
---
Cc: "Uwe Kleine-König" <ukleinek@kernel.org>
Cc: Conor Dooley <conor+dt@kernel.org>
Cc: Krzysztof Kozlowski <krzk+dt@kernel.org>
Cc: Rob Herring <robh@kernel.org>
Cc: devicetree@vger.kernel.org
Cc: linux-pwm@vger.kernel.org
Cc: linux-renesas-soc@vger.kernel.org
---
V2: - Switch to waveform ops
    - Add shutdown hook to force the fan to maximum RPM on shutdown
      instead of stopping it, to be on the safe side
V3: - Find the 30 kHz fixed period PWM, use that
    - Add comments
    - Consolidate argon_fan_hat_write()
V4: - Add if (wf->duty_length_ns > ARGON40_FAN_HAT_PERIOD_NS) overflow check
    - Use i2c_smbus_write_byte_data()
    - Rename struct pwm_chip *pc to struct pwm_chip *chip
    - Remove tab alignment from argon_fan_hat_pwm_ops {}
    - Define ARGON40_FAN_HAT_REG_DUTY_CYCLE macro
V5: - Undo "Add shutdown hook" from V2
---
 drivers/pwm/Kconfig             |   9 +++
 drivers/pwm/Makefile            |   1 +
 drivers/pwm/pwm-argon-fan-hat.c | 109 ++++++++++++++++++++++++++++++++
 3 files changed, 119 insertions(+)
 create mode 100644 drivers/pwm/pwm-argon-fan-hat.c

diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index 6e113f8b4baf..3ef1757502eb 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -66,6 +66,15 @@ config PWM_APPLE
 	  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
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index 96160f4257fc..ff4f47e5fb7a 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -3,6 +3,7 @@ obj-$(CONFIG_PWM)		+= core.o
 obj-$(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
diff --git a/drivers/pwm/pwm-argon-fan-hat.c b/drivers/pwm/pwm-argon-fan-hat.c
new file mode 100644
index 000000000000..2c59bd142d40
--- /dev/null
+++ b/drivers/pwm/pwm-argon-fan-hat.c
@@ -0,0 +1,109 @@
+// 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 <marek.vasut+renesas@mailbox.org>");
+MODULE_DESCRIPTION("Argon40 Fan HAT");
+MODULE_LICENSE("GPL");
-- 
2.47.2