Hi Christian,
On Wed, Mar 13, 2019 at 05:35:38PM +0000, Grönke, Christian wrote:
[ ... ]
> >
> > Our last e-mails overlapped; can you explore what it would take to add
> > support for ieee754 half precision floating point ? We would need a new
> > set of conversion functions in the core (ie pmbus_reg2data_ieee754 and
> > pmbus_data2reg_ieee754), and your driver would have to implement the
> > linear11 <-> ieee754 conversion. That may be a bit more work, but it
> > would also be cleaner, and it should not affect precision.
>
> I give it a look tomorrow. If this presents a proper and clean way,
> to avoid adding the hack in the generic code it might be worth it.
>
Please use the attached patch as starting point. Obviously I could not do much
testing, but unit testing returned reasonable results. Note that we don't have
to follow the pmbus spec to the letter - it is sufficient to declare the VOUT
values to be in ieee754 format for your driver.
Guenter
---
>From 2f80cad52914c674afc5a80a84f4756e1b12d803 Mon Sep 17 00:00:00 2001
From: Guenter Roeck <linux@xxxxxxxxxxxx>
Date: Wed, 13 Mar 2019 14:36:28 -0700
Subject: [PATCH] hwmon: (pmbus) Add IEEE 754 half precision support to PMBus
core
PMBus v1.3.1 adds IEEE 754 half precision as additional data format.
Add support for it.
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
---
drivers/hwmon/pmbus/pmbus.h | 2 +-
drivers/hwmon/pmbus/pmbus_core.c | 135 +++++++++++++++++++++++++++++++++++++--
2 files changed, 132 insertions(+), 5 deletions(-)
diff --git a/drivers/hwmon/pmbus/pmbus.h b/drivers/hwmon/pmbus/pmbus.h
index 1d24397d36ec..6477eb433790 100644
--- a/drivers/hwmon/pmbus/pmbus.h
+++ b/drivers/hwmon/pmbus/pmbus.h
@@ -374,7 +374,7 @@ enum pmbus_sensor_classes {
#define PMBUS_PAGE_VIRTUAL BIT(31)
-enum pmbus_data_format { linear = 0, direct, vid };
+enum pmbus_data_format { linear = 0, ieee754, direct, vid };
enum vrm_version { vr11 = 0, vr12, vr13 };
struct pmbus_driver_info {
diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
index 2e2b5851139c..e828160a1793 100644
--- a/drivers/hwmon/pmbus/pmbus_core.c
+++ b/drivers/hwmon/pmbus/pmbus_core.c
@@ -619,6 +619,66 @@ static struct pmbus_data *pmbus_update_device(struct device *dev)
}
/*
+ * 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.
*/
@@ -740,6 +800,9 @@ static long 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);
@@ -748,8 +811,65 @@ static long 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 resulting number is within range */
+ 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, long val)
@@ -795,12 +915,12 @@ static u16 pmbus_data2reg_linear(struct pmbus_data *data,
val = val * 1000;
/* 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;
}
@@ -878,6 +998,9 @@ 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);
@@ -1967,6 +2090,10 @@ 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;
}
--
2.7.4
