hwmon: (pmbus/max31785) Add fan control

The implementation makes use of the new fan control virtual registers
exposed by the pmbus core. It mixes use of the default implementations
with some overrides via the read/write handlers to handle FAN_COMMAND_1
on the MAX31785, whose definition breaks the value range into various
control bands dependent on RPM or PWM mode.
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/max31785

@@ -32,6 +32,7 @@ Sysfs attributes
 fan[1-4]_alarm		Fan alarm.
 fan[1-4]_fault		Fan fault.
 fan[1-4]_input		Fan RPM.
+fan[1-4]_target		Fan input target
 
 in[1-6]_crit		Critical maximum output voltage
 in[1-6]_crit_alarm	Output voltage critical high alarm
@@ -44,6 +45,12 @@ in[1-6]_max_alarm	Output voltage high alarm
 in[1-6]_min		Minimum output voltage
 in[1-6]_min_alarm	Output voltage low alarm
 
+pwm[1-4]		Fan target duty cycle (0..255)
+pwm[1-4]_enable		0: Full-speed
+			1: Manual PWM control
+			2: Automatic PWM (tach-feedback RPM fan-control)
+			3: Automatic closed-loop (temp-feedback fan-control)
+
 temp[1-11]_crit		Critical high temperature
 temp[1-11]_crit_alarm	Chip temperature critical high alarm
 temp[1-11]_input	Measured temperature

drivers/hwmon/pmbus/max31785.c

@@ -20,8 +20,136 @@ enum max31785_regs {
 
 #define MAX31785_NR_PAGES		23
 
+static int max31785_get_pwm(struct i2c_client *client, int page)
+{
+	int rv;
+
+	rv = pmbus_get_fan_rate_device(client, page, 0, percent);
+	if (rv < 0)
+		return rv;
+	else if (rv >= 0x8000)
+		return 0;
+	else if (rv >= 0x2711)
+		return 0x2710;
+
+	return rv;
+}
+
+static int max31785_get_pwm_mode(struct i2c_client *client, int page)
+{
+	int config;
+	int command;
+
+	config = pmbus_read_byte_data(client, page, PMBUS_FAN_CONFIG_12);
+	if (config < 0)
+		return config;
+
+	command = pmbus_read_word_data(client, page, PMBUS_FAN_COMMAND_1);
+	if (command < 0)
+		return command;
+
+	if (config & PB_FAN_1_RPM)
+		return (command >= 0x8000) ? 3 : 2;
+
+	if (command >= 0x8000)
+		return 3;
+	else if (command >= 0x2711)
+		return 0;
+
+	return 1;
+}
+
+static int max31785_read_word_data(struct i2c_client *client, int page,
+				   int reg)
+{
+	int rv;
+
+	switch (reg) {
+	case PMBUS_VIRT_PWM_1:
+		rv = max31785_get_pwm(client, page);
+		break;
+	case PMBUS_VIRT_PWM_ENABLE_1:
+		rv = max31785_get_pwm_mode(client, page);
+		break;
+	default:
+		rv = -ENODATA;
+		break;
+	}
+
+	return rv;
+}
+
+static inline u32 max31785_scale_pwm(u32 sensor_val)
+{
+	/*
+	 * The datasheet describes the accepted value range for manual PWM as
+	 * [0, 0x2710], while the hwmon pwmX sysfs interface accepts values in
+	 * [0, 255]. The MAX31785 uses DIRECT mode to scale the FAN_COMMAND
+	 * registers and in PWM mode the coefficients are m=1, b=0, R=2. The
+	 * important observation here is that 0x2710 == 10000 == 100 * 100.
+	 *
+	 * R=2 (== 10^2 == 100) accounts for scaling the value provided at the
+	 * sysfs interface into the required hardware resolution, but it does
+	 * not yet yield a value that we can write to the device (this initial
+	 * scaling is handled by pmbus_data2reg()). Multiplying by 100 below
+	 * translates the parameter value into the percentage units required by
+	 * PMBus, and then we scale back by 255 as required by the hwmon pwmX
+	 * interface to yield the percentage value at the appropriate
+	 * resolution for hardware.
+	 */
+	return (sensor_val * 100) / 255;
+}
+
+static int max31785_pwm_enable(struct i2c_client *client, int page,
+				    u16 word)
+{
+	int config = 0;
+	int rate;
+
+	switch (word) {
+	case 0:
+		rate = 0x7fff;
+		break;
+	case 1:
+		rate = pmbus_get_fan_rate_cached(client, page, 0, percent);
+		if (rate < 0)
+			return rate;
+		rate = max31785_scale_pwm(rate);
+		break;
+	case 2:
+		config = PB_FAN_1_RPM;
+		rate = pmbus_get_fan_rate_cached(client, page, 0, rpm);
+		if (rate < 0)
+			return rate;
+		break;
+	case 3:
+		rate = 0xffff;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return pmbus_update_fan(client, page, 0, config, PB_FAN_1_RPM, rate);
+}
+
+static int max31785_write_word_data(struct i2c_client *client, int page,
+				    int reg, u16 word)
+{
+	switch (reg) {
+	case PMBUS_VIRT_PWM_1:
+		return pmbus_update_fan(client, page, 0, 0, PB_FAN_1_RPM,
+					max31785_scale_pwm(word));
+	case PMBUS_VIRT_PWM_ENABLE_1:
+		return max31785_pwm_enable(client, page, word);
+	default:
+		break;
+	}
+
+	return -ENODATA;
+}
+
 #define MAX31785_FAN_FUNCS \
-	(PMBUS_HAVE_FAN12 | PMBUS_HAVE_STATUS_FAN12)
+	(PMBUS_HAVE_FAN12 | PMBUS_HAVE_STATUS_FAN12 | PMBUS_HAVE_PWM12)
 
 #define MAX31785_TEMP_FUNCS \
 	(PMBUS_HAVE_TEMP | PMBUS_HAVE_STATUS_TEMP)
@@ -32,11 +160,19 @@ enum max31785_regs {
 static const struct pmbus_driver_info max31785_info = {
 	.pages = MAX31785_NR_PAGES,
 
+	.write_word_data = max31785_write_word_data,
+	.read_word_data = max31785_read_word_data,
+
 	/* RPM */
 	.format[PSC_FAN] = direct,
 	.m[PSC_FAN] = 1,
 	.b[PSC_FAN] = 0,
 	.R[PSC_FAN] = 0,
+	/* PWM */
+	.format[PSC_PWM] = direct,
+	.m[PSC_PWM] = 1,
+	.b[PSC_PWM] = 0,
+	.R[PSC_PWM] = 2,
 	.func[0] = MAX31785_FAN_FUNCS,
 	.func[1] = MAX31785_FAN_FUNCS,
 	.func[2] = MAX31785_FAN_FUNCS,