hwmon: (amc6821) Add support for pwm1_mode attribute

AMC6821 supports configuring if a fan is DC or PWM controlled.
Add support for the pwm1_mode attribute to make it runtime configurable.
Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/amc6821.rst

@@ -58,6 +58,7 @@ pwm1_enable		rw	regulator mode, 1=open loop, 2=fan controlled
 				remote-sensor temperature,
 				4=fan controlled by target rpm set with
 				fan1_target attribute.
+pwm1_mode		rw	Fan duty control mode (0=DC, 1=PWM)
 pwm1_auto_channels_temp ro	1 if pwm_enable==2, 3 if pwm_enable==3
 pwm1_auto_point1_pwm	ro	Hardwired to 0, shared for both
 				temperature channels.

drivers/hwmon/amc6821.c

@@ -312,6 +312,12 @@ static int amc6821_pwm_read(struct device *dev, u32 attr, long *val)
 			break;
 		}
 		return 0;
+	case hwmon_pwm_mode:
+		err = regmap_read(regmap, AMC6821_REG_CONF2, &regval);
+		if (err)
+			return err;
+		*val = !!(regval & AMC6821_CONF2_TACH_MODE);
+		return 0;
 	case hwmon_pwm_auto_channels_temp:
 		err = regmap_read(regmap, AMC6821_REG_CONF1, &regval);
 		if (err)
@@ -367,6 +373,13 @@ static int amc6821_pwm_write(struct device *dev, u32 attr, long val)
 		return regmap_update_bits(regmap, AMC6821_REG_CONF1,
 					  AMC6821_CONF1_FDRC0 | AMC6821_CONF1_FDRC1,
 					  mode);
+	case hwmon_pwm_mode:
+		if (val < 0 || val > 1)
+			return -EINVAL;
+		return regmap_update_bits(regmap, AMC6821_REG_CONF2,
+					  AMC6821_CONF2_TACH_MODE,
+					  val ? AMC6821_CONF2_TACH_MODE : 0);
+		break;
 	case hwmon_pwm_input:
 		if (val < 0 || val > 255)
 			return -EINVAL;
@@ -748,6 +761,7 @@ static umode_t amc6821_is_visible(const void *data,
 		}
 	case hwmon_pwm:
 		switch (attr) {
+		case hwmon_pwm_mode:
 		case hwmon_pwm_enable:
 		case hwmon_pwm_input:
 			return 0644;
@@ -774,7 +788,7 @@ static const struct hwmon_channel_info * const amc6821_info[] = {
 			   HWMON_F_INPUT | HWMON_F_MIN | HWMON_F_MAX |
 			   HWMON_F_TARGET | HWMON_F_PULSES | HWMON_F_FAULT),
 	HWMON_CHANNEL_INFO(pwm,
-			   HWMON_PWM_INPUT | HWMON_PWM_ENABLE |
+			   HWMON_PWM_INPUT | HWMON_PWM_ENABLE | HWMON_PWM_MODE |
 			   HWMON_PWM_AUTO_CHANNELS_TEMP),
 	NULL
 };