Commit 4036a48e authored by Guenter Roeck's avatar Guenter Roeck
Browse files

hwmon: (pmbus) Add IEEE 754 half precision support to PMBus core 



Add support for the IEEE 754 half precision data format as specified
in PMBus v1.3.1.

Signed-off-by: default avatarGuenter Roeck <linux@roeck-us.net>
parent ca99633a

drivers/hwmon/pmbus/pmbus.h

+1 −1
Original line number Diff line number Diff line
@@ -406,7 +406,7 @@ enum pmbus_sensor_classes { 
#define PMBUS_PHASE_VIRTUAL	BIT(30)	/* Phases on this page are virtual */

#define PMBUS_PAGE_VIRTUAL	BIT(31)	/* Page is virtual */



enum pmbus_data_format { linear = 0, direct, vid };

enum pmbus_data_format { linear = 0, ieee754, direct, vid };

enum vrm_version { vr11 = 0, vr12, vr13, imvp9, amd625mv };



struct pmbus_driver_info {

drivers/hwmon/pmbus/pmbus_core.c

+138 −4
Original line number Diff line number Diff line
@@ -611,6 +611,66 @@ static void pmbus_update_sensor_data(struct i2c_client *client, struct pmbus_sen 
						     sensor->phase, sensor->reg);

}



/*

 * Convert ieee754 sensor values to milli- or micro-units

 * depending on sensor type.

 *

 * ieee754 data format:

 *	bit 15:		sign

 *	bit 10..14:	exponent

 *	bit 0..9:	mantissa

 * exponent=0:

 *	v=(−1)^signbit * 2^(−14) * 0.significantbits

 * exponent=1..30:

 *	v=(−1)^signbit * 2^(exponent - 15) * 1.significantbits

 * exponent=31:

 *	v=NaN

 *

 * Add the number mantissa bits into the calculations for simplicity.

 * To do that, add '10' to the exponent. By doing that, we can just add

 * 0x400 to normal values and get the expected result.

 */

static long pmbus_reg2data_ieee754(struct pmbus_data *data,

				   struct pmbus_sensor *sensor)

{

	int exponent;

	bool sign;

	long val;



	/* only support half precision for now */

	sign = sensor->data & 0x8000;

	exponent = (sensor->data >> 10) & 0x1f;

	val = sensor->data & 0x3ff;



	if (exponent == 0) {			/* subnormal */

		exponent = -(14 + 10);

	} else if (exponent ==  0x1f) {		/* NaN, convert to min/max */

		exponent = 0;

		val = 65504;

	} else {

		exponent -= (15 + 10);		/* normal */

		val |= 0x400;

	}



	/* scale result to milli-units for all sensors except fans */

	if (sensor->class != PSC_FAN)

		val = val * 1000L;



	/* scale result to micro-units for power sensors */

	if (sensor->class == PSC_POWER)

		val = val * 1000L;



	if (exponent >= 0)

		val <<= exponent;

	else

		val >>= -exponent;



	if (sign)

		val = -val;



	return val;

}



/*

 * Convert linear sensor values to milli- or micro-units

 * depending on sensor type.
@@ -741,6 +801,9 @@ static s64 pmbus_reg2data(struct pmbus_data *data, struct pmbus_sensor *sensor) 
	case vid:

		val = pmbus_reg2data_vid(data, sensor);

		break;

	case ieee754:

		val = pmbus_reg2data_ieee754(data, sensor);

		break;

	case linear:

	default:

		val = pmbus_reg2data_linear(data, sensor);
@@ -749,8 +812,72 @@ static s64 pmbus_reg2data(struct pmbus_data *data, struct pmbus_sensor *sensor) 
	return val;

}



#define MAX_MANTISSA	(1023 * 1000)

#define MIN_MANTISSA	(511 * 1000)

#define MAX_IEEE_MANTISSA	(0x7ff * 1000)

#define MIN_IEEE_MANTISSA	(0x400 * 1000)



static u16 pmbus_data2reg_ieee754(struct pmbus_data *data,

				  struct pmbus_sensor *sensor, long val)

{

	u16 exponent = (15 + 10);

	long mantissa;

	u16 sign = 0;



	/* simple case */

	if (val == 0)

		return 0;



	if (val < 0) {

		sign = 0x8000;

		val = -val;

	}



	/* Power is in uW. Convert to mW before converting. */

	if (sensor->class == PSC_POWER)

		val = DIV_ROUND_CLOSEST(val, 1000L);



	/*

	 * For simplicity, convert fan data to milli-units

	 * before calculating the exponent.

	 */

	if (sensor->class == PSC_FAN)

		val = val * 1000;



	/* Reduce large mantissa until it fits into 10 bit */

	while (val > MAX_IEEE_MANTISSA && exponent < 30) {

		exponent++;

		val >>= 1;

	}

	/*

	 * Increase small mantissa to generate valid 'normal'

	 * number

	 */

	while (val < MIN_IEEE_MANTISSA && exponent > 1) {

		exponent--;

		val <<= 1;

	}



	/* Convert mantissa from milli-units to units */

	mantissa = DIV_ROUND_CLOSEST(val, 1000);



	/*

	 * Ensure that the resulting number is within range.

	 * Valid range is 0x400..0x7ff, where bit 10 reflects

	 * the implied high bit in normalized ieee754 numbers.

	 * Set the range to 0x400..0x7ff to reflect this.

	 * The upper bit is then removed by the mask against

	 * 0x3ff in the final assignment.

	 */

	if (mantissa > 0x7ff)

		mantissa = 0x7ff;

	else if (mantissa < 0x400)

		mantissa = 0x400;



	/* Convert to sign, 5 bit exponent, 10 bit mantissa */

	return sign | (mantissa & 0x3ff) | ((exponent << 10) & 0x7c00);

}



#define MAX_LIN_MANTISSA	(1023 * 1000)

#define MIN_LIN_MANTISSA	(511 * 1000)



static u16 pmbus_data2reg_linear(struct pmbus_data *data,

				 struct pmbus_sensor *sensor, s64 val)
@@ -796,12 +923,12 @@ static u16 pmbus_data2reg_linear(struct pmbus_data *data, 
		val = val * 1000LL;



	/* Reduce large mantissa until it fits into 10 bit */

	while (val >= MAX_MANTISSA && exponent < 15) {

	while (val >= MAX_LIN_MANTISSA && exponent < 15) {

		exponent++;

		val >>= 1;

	}

	/* Increase small mantissa to improve precision */

	while (val < MIN_MANTISSA && exponent > -15) {

	while (val < MIN_LIN_MANTISSA && exponent > -15) {

		exponent--;

		val <<= 1;

	}
@@ -875,6 +1002,9 @@ static u16 pmbus_data2reg(struct pmbus_data *data, 
	case vid:

		regval = pmbus_data2reg_vid(data, sensor, val);

		break;

	case ieee754:

		regval = pmbus_data2reg_ieee754(data, sensor, val);

		break;

	case linear:

	default:

		regval = pmbus_data2reg_linear(data, sensor, val);
@@ -2369,6 +2499,10 @@ static int pmbus_identify_common(struct i2c_client *client, 
			if (data->info->format[PSC_VOLTAGE_OUT] != direct)

				return -ENODEV;

			break;

		case 3:	/* ieee 754 half precision */

			if (data->info->format[PSC_VOLTAGE_OUT] != ieee754)

				return -ENODEV;

			break;

		default:

			return -ENODEV;

		}