[hwmon-next PATCH v4 3/4] hwmon: (adt7470) Expose fan control via PWM framework

[Luiz Angelo Daros de Luca]

The ADT7470 features four PWM outputs designed to control fans.
Previously, these were only accessible through the legacy hwmon
sysfs interface.

Expose the ADT7470 fan control lines through the generic PWM framework.
This allows generic PWM consumers described in Device Tree, such as
"pwm-fan", to use the device through the "#pwm-cells" property.  This is
particularly necessary for boards where the ADT7470 external temperature
sensors are not populated and the chip is used strictly as a fan
controller (e.g., Edgecore ECS-2100-52T switches). In such setups,
delegating control to the generic PWM subsystem allows the kernel's
thermal framework to manage the fans based on unrelated temperature
zones, such as internal SoC sensors.

When a PWM consumer applies a new PWM state, the driver automatically
switches the corresponding PWM channel to manual mode so that the
requested duty cycle takes effect. The duty cycle specified by the PWM
framework is internally converted to the 0-255 scale expected by the
hardware registers.

The legacy sysfs interface remains unaffected and operates in parallel.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@xxxxxxxxx>
---
 drivers/hwmon/Kconfig   |   1 +
 drivers/hwmon/adt7470.c | 137 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 138 insertions(+)

diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 6b71e3304b4f..0d6bd117d14d 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -224,6 +224,7 @@ config SENSORS_ADT7462
 config SENSORS_ADT7470
 	tristate "Analog Devices ADT7470"
 	depends on I2C
+	depends on PWM || PWM=n
 	select REGMAP_I2C
 	help
 	  If you say yes here you get support for the Analog Devices
diff --git a/drivers/hwmon/adt7470.c b/drivers/hwmon/adt7470.c
index 87ddd7b8ddae..883838fdcd7d 100644
--- a/drivers/hwmon/adt7470.c
+++ b/drivers/hwmon/adt7470.c
@@ -22,6 +22,9 @@
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/util_macros.h>
+#include <linux/pwm.h>
+#include <linux/cleanup.h>
+#include <linux/math64.h>
 
 /* Addresses to scan */
 static const unsigned short normal_i2c[] = { 0x2C, 0x2E, 0x2F, I2C_CLIENT_END };
@@ -887,6 +890,125 @@ static int adt7470_pwm_write(struct device *dev, u32 attr, int channel, long val
 	return err;
 }
 
+struct adt7470_pwm_wfhw {
+	u8 val;
+};
+
+static int adt7470_pwm_round_waveform_tohw(struct pwm_chip *chip,
+					   struct pwm_device *pwm,
+					   const struct pwm_waveform *wf,
+					   void *_wfhw)
+{
+	struct adt7470_data *data = pwmchip_get_drvdata(chip);
+	struct adt7470_pwm_wfhw *wfhw = _wfhw;
+	u64 period_ns;
+
+	if (wf->duty_length_ns == 0) {
+		wfhw->val = 0;
+		return 0;
+	}
+
+	/*
+	 * The PWM frequency (period) is a single chip-wide setting shared by
+	 * all 4 channels, so it cannot be changed on a per-pwm_device basis
+	 * through this API. The duty cycle is rounded against the currently
+	 * configured hardware period rather than the period requested in
+	 * @wf; round_waveform_fromhw() reports the actual resulting
+	 * waveform back so the core/consumer can detect a mismatch.
+	 */
+	period_ns = DIV_ROUND_CLOSEST(NSEC_PER_SEC, data->pwm_freq);
+	wfhw->val = min_t(u64,
+			  mul_u64_u64_div_u64(wf->duty_length_ns, ADT7470_PWM_MAX, period_ns),
+			  ADT7470_PWM_MAX);
+	return 0;
+}
+
+static int adt7470_pwm_round_waveform_fromhw(struct pwm_chip *chip,
+					     struct pwm_device *pwm,
+					     const void *_wfhw,
+					     struct pwm_waveform *wf)
+{
+	struct adt7470_data *data = pwmchip_get_drvdata(chip);
+	const struct adt7470_pwm_wfhw *wfhw = _wfhw;
+
+	wf->period_length_ns = DIV_ROUND_CLOSEST(NSEC_PER_SEC, data->pwm_freq);
+	wf->duty_offset_ns = 0;
+	wf->duty_length_ns = mul_u64_u64_div_u64(wfhw->val,
+						 wf->period_length_ns,
+						 ADT7470_PWM_MAX);
+
+	return 0;
+}
+
+static int adt7470_pwm_read_waveform(struct pwm_chip *chip,
+				     struct pwm_device *pwm,
+				     void *_wfhw)
+{
+	struct adt7470_data *data = pwmchip_get_drvdata(chip);
+	struct device *dev = regmap_get_device(data->regmap);
+	struct adt7470_pwm_wfhw *wfhw = _wfhw;
+
+	data = adt7470_update_device(dev);
+	if (IS_ERR(data))
+		return PTR_ERR(data);
+
+	/*
+	 * No lock needed: like the other hwmon_ops read callbacks in this
+	 * driver (e.g. adt7470_pwm_read()), this only does a single byte
+	 * read from the cache populated by adt7470_update_device().
+	 */
+	wfhw->val = data->pwm[pwm->hwpwm];
+
+	return 0;
+}
+
+static int adt7470_pwm_write_waveform(struct pwm_chip *chip,
+				      struct pwm_device *pwm,
+				      const void *_wfhw)
+{
+	struct adt7470_data *data = pwmchip_get_drvdata(chip);
+	const struct adt7470_pwm_wfhw *wfhw = _wfhw;
+	unsigned int pwm_auto_reg_mask;
+	int err;
+
+	if (pwm->hwpwm % 2)
+		pwm_auto_reg_mask = ADT7470_PWM2_AUTO_MASK;
+	else
+		pwm_auto_reg_mask = ADT7470_PWM1_AUTO_MASK;
+
+	guard(mutex)(&data->lock);
+
+	if (data->pwm[pwm->hwpwm] == wfhw->val &&
+	    data->pwm_automatic[pwm->hwpwm] == 0)
+		return 0;
+
+	/* Put the PWM channel in manual mode before updating it. */
+	err = regmap_update_bits(data->regmap,
+				 ADT7470_REG_PWM_CFG(pwm->hwpwm),
+				 pwm_auto_reg_mask, 0);
+	if (err < 0)
+		return err;
+
+	data->pwm_automatic[pwm->hwpwm] = 0;
+
+	err = regmap_write(data->regmap,
+			   ADT7470_REG_PWM(pwm->hwpwm), wfhw->val);
+	if (err < 0)
+		return err;
+
+	data->pwm[pwm->hwpwm] = wfhw->val;
+
+	return 0;
+}
+
+static const struct pwm_ops adt7470_pwm_ops = {
+	.sizeof_wfhw = sizeof(struct adt7470_pwm_wfhw),
+	.round_waveform_tohw = adt7470_pwm_round_waveform_tohw,
+	.round_waveform_fromhw = adt7470_pwm_round_waveform_fromhw,
+	.read_waveform = adt7470_pwm_read_waveform,
+	.write_waveform = adt7470_pwm_write_waveform,
+};
+
 static ssize_t pwm_max_show(struct device *dev,
 			    struct device_attribute *devattr, char *buf)
 {
@@ -1336,6 +1458,21 @@ static int adt7470_probe(struct i2c_client *client)
 	if (IS_ERR(hwmon_dev))
 		return PTR_ERR(hwmon_dev);
 
+	if (IS_REACHABLE(CONFIG_PWM)) {
+		struct pwm_chip *chip;
+
+		chip = devm_pwmchip_alloc(dev, ADT7470_PWM_COUNT, 0);
+		if (IS_ERR(chip))
+			return PTR_ERR(chip);
+
+		chip->ops = &adt7470_pwm_ops;
+		pwmchip_set_drvdata(chip, data);
+
+		err = devm_pwmchip_add(dev, chip);
+		if (err)
+			return dev_err_probe(dev, err, "failed to register PWM chip\n");
+	}
+
 	data->auto_update = kthread_run(adt7470_update_thread, client, "%s",
 					dev_name(hwmon_dev));
 	if (IS_ERR(data->auto_update))

-- 
2.55.0