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: Guenter Roeck <linux@roeck-us.net>
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@ -406,7 +406,7 @@ enum pmbus_sensor_classes {
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#define PMBUS_PHASE_VIRTUAL BIT(30) /* Phases on this page are virtual */
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#define PMBUS_PAGE_VIRTUAL BIT(31) /* Page is virtual */
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enum pmbus_data_format { linear = 0, direct, vid };
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enum pmbus_data_format { linear = 0, ieee754, direct, vid };
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enum vrm_version { vr11 = 0, vr12, vr13, imvp9, amd625mv };
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struct pmbus_driver_info {
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@ -611,6 +611,66 @@ static void pmbus_update_sensor_data(struct i2c_client *client, struct pmbus_sen
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sensor->phase, sensor->reg);
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}
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/*
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* Convert ieee754 sensor values to milli- or micro-units
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* depending on sensor type.
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*
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* ieee754 data format:
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* bit 15: sign
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* bit 10..14: exponent
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* bit 0..9: mantissa
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* exponent=0:
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* v=(−1)^signbit * 2^(−14) * 0.significantbits
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* exponent=1..30:
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* v=(−1)^signbit * 2^(exponent - 15) * 1.significantbits
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* exponent=31:
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* v=NaN
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*
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* Add the number mantissa bits into the calculations for simplicity.
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* To do that, add '10' to the exponent. By doing that, we can just add
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* 0x400 to normal values and get the expected result.
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*/
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static long pmbus_reg2data_ieee754(struct pmbus_data *data,
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struct pmbus_sensor *sensor)
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{
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int exponent;
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bool sign;
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long val;
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/* only support half precision for now */
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sign = sensor->data & 0x8000;
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exponent = (sensor->data >> 10) & 0x1f;
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val = sensor->data & 0x3ff;
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if (exponent == 0) { /* subnormal */
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exponent = -(14 + 10);
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} else if (exponent == 0x1f) { /* NaN, convert to min/max */
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exponent = 0;
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val = 65504;
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} else {
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exponent -= (15 + 10); /* normal */
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val |= 0x400;
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}
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/* scale result to milli-units for all sensors except fans */
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if (sensor->class != PSC_FAN)
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val = val * 1000L;
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/* scale result to micro-units for power sensors */
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if (sensor->class == PSC_POWER)
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val = val * 1000L;
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if (exponent >= 0)
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val <<= exponent;
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else
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val >>= -exponent;
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if (sign)
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val = -val;
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return val;
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}
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/*
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* Convert linear sensor values to milli- or micro-units
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* depending on sensor type.
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@ -741,6 +801,9 @@ static s64 pmbus_reg2data(struct pmbus_data *data, struct pmbus_sensor *sensor)
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case vid:
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val = pmbus_reg2data_vid(data, sensor);
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break;
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case ieee754:
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val = pmbus_reg2data_ieee754(data, sensor);
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break;
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case linear:
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default:
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val = pmbus_reg2data_linear(data, sensor);
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@ -749,8 +812,72 @@ static s64 pmbus_reg2data(struct pmbus_data *data, struct pmbus_sensor *sensor)
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return val;
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}
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#define MAX_MANTISSA (1023 * 1000)
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#define MIN_MANTISSA (511 * 1000)
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#define MAX_IEEE_MANTISSA (0x7ff * 1000)
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#define MIN_IEEE_MANTISSA (0x400 * 1000)
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static u16 pmbus_data2reg_ieee754(struct pmbus_data *data,
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struct pmbus_sensor *sensor, long val)
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{
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u16 exponent = (15 + 10);
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long mantissa;
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u16 sign = 0;
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/* simple case */
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if (val == 0)
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return 0;
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if (val < 0) {
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sign = 0x8000;
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val = -val;
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}
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/* Power is in uW. Convert to mW before converting. */
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if (sensor->class == PSC_POWER)
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val = DIV_ROUND_CLOSEST(val, 1000L);
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/*
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* For simplicity, convert fan data to milli-units
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* before calculating the exponent.
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*/
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if (sensor->class == PSC_FAN)
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val = val * 1000;
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/* Reduce large mantissa until it fits into 10 bit */
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while (val > MAX_IEEE_MANTISSA && exponent < 30) {
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exponent++;
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val >>= 1;
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}
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/*
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* Increase small mantissa to generate valid 'normal'
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* number
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*/
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while (val < MIN_IEEE_MANTISSA && exponent > 1) {
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exponent--;
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val <<= 1;
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}
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/* Convert mantissa from milli-units to units */
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mantissa = DIV_ROUND_CLOSEST(val, 1000);
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/*
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* Ensure that the resulting number is within range.
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* Valid range is 0x400..0x7ff, where bit 10 reflects
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* the implied high bit in normalized ieee754 numbers.
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* Set the range to 0x400..0x7ff to reflect this.
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* The upper bit is then removed by the mask against
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* 0x3ff in the final assignment.
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*/
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if (mantissa > 0x7ff)
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mantissa = 0x7ff;
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else if (mantissa < 0x400)
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mantissa = 0x400;
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/* Convert to sign, 5 bit exponent, 10 bit mantissa */
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return sign | (mantissa & 0x3ff) | ((exponent << 10) & 0x7c00);
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}
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#define MAX_LIN_MANTISSA (1023 * 1000)
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#define MIN_LIN_MANTISSA (511 * 1000)
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static u16 pmbus_data2reg_linear(struct pmbus_data *data,
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struct pmbus_sensor *sensor, s64 val)
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@ -796,12 +923,12 @@ static u16 pmbus_data2reg_linear(struct pmbus_data *data,
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val = val * 1000LL;
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/* Reduce large mantissa until it fits into 10 bit */
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while (val >= MAX_MANTISSA && exponent < 15) {
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while (val >= MAX_LIN_MANTISSA && exponent < 15) {
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exponent++;
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val >>= 1;
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}
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/* Increase small mantissa to improve precision */
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while (val < MIN_MANTISSA && exponent > -15) {
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while (val < MIN_LIN_MANTISSA && exponent > -15) {
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exponent--;
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val <<= 1;
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}
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@ -875,6 +1002,9 @@ static u16 pmbus_data2reg(struct pmbus_data *data,
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case vid:
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regval = pmbus_data2reg_vid(data, sensor, val);
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break;
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case ieee754:
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regval = pmbus_data2reg_ieee754(data, sensor, val);
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break;
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case linear:
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default:
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regval = pmbus_data2reg_linear(data, sensor, val);
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@ -2369,6 +2499,10 @@ static int pmbus_identify_common(struct i2c_client *client,
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if (data->info->format[PSC_VOLTAGE_OUT] != direct)
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return -ENODEV;
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break;
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case 3: /* ieee 754 half precision */
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if (data->info->format[PSC_VOLTAGE_OUT] != ieee754)
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return -ENODEV;
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break;
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default:
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return -ENODEV;
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}
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