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>
This commit is contained in:
Guenter Roeck 2019-03-13 14:36:28 -07:00
parent ca99633ae4
commit 4036a48e20
2 changed files with 139 additions and 5 deletions

View File

@ -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 {

View File

@ -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;
}