[PATCH 4/4] hwmon: (pmbus/tps40422) add support for output voltage margining

[Ruslan Babayev <ruslan@babayev.com>]

TPS40422 has MFR_SPECIFIC registers STEP_VREF_MARGIN_HIGH and
STEP_VREF_MARGIN_LOW, which are signed 16-bit in units of 2mV. This
value is an offset from the nominal reference voltage of 600mV.

For instance, the default value of STEP_VREF_MARGIN_LOW is -30
(decimal), which corresponds to a default margin low voltage of
600 - 30 * 2 = 540mV.

Introduce tps40422_{read/write}_word_data() callbacks to map the
MFR_SPECIFIC registers to standard PMBUS_VOUT_MARGIN_HIGH and
PMBUS_VOUT_MARGIN_LOW. For the latter, pmbus_core stores sensor data
in linear16 format as specified in VOUT_MODE.  Note, that on TPS40422
the exponent is fixed at (-9). The callbacks will perform the
necessary conversions.

Cc: xe-linux-external@cisco.com
Signed-off-by: Ruslan Babayev <ruslan@babayev.com>
---
 drivers/hwmon/pmbus/tps40422.c | 54 ++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/drivers/hwmon/pmbus/tps40422.c b/drivers/hwmon/pmbus/tps40422.c
index 32803825d47e..129d1b0e6b43 100644
--- a/drivers/hwmon/pmbus/tps40422.c
+++ b/drivers/hwmon/pmbus/tps40422.c
@@ -21,16 +21,70 @@
 #include <linux/i2c.h>
 #include "pmbus.h"
 
+#define TPS40422_STEP_VREF_MARGIN_HIGH	0xd5
+#define TPS40422_STEP_VREF_MARGIN_LOW	0xd6
+#define TPS40422_VREF			600
+
+static int tps40422_read_word_data(struct i2c_client *client, int page, int reg)
+{
+	int ret;
+
+	switch (reg) {
+	case PMBUS_VOUT_MARGIN_HIGH:
+		reg = TPS40422_STEP_VREF_MARGIN_HIGH;
+		break;
+	case PMBUS_VOUT_MARGIN_LOW:
+		reg = TPS40422_STEP_VREF_MARGIN_LOW;
+		break;
+	default:
+		return -ENODATA;
+	}
+
+	ret = pmbus_read_word_data(client, page, reg);
+	if (ret < 0)
+		return ret;
+
+	ret = (TPS40422_VREF + ((s16)ret) * 2) << 9;
+	ret = DIV_ROUND_CLOSEST(ret, 1000);
+
+	return ret;
+}
+
+static int tps40422_write_word_data(struct i2c_client *client, int page,
+				    int reg, u16 word)
+{
+	u16 val;
+
+	switch (reg) {
+	case PMBUS_VOUT_MARGIN_HIGH:
+		reg = TPS40422_STEP_VREF_MARGIN_HIGH;
+		break;
+	case PMBUS_VOUT_MARGIN_LOW:
+		reg = TPS40422_STEP_VREF_MARGIN_LOW;
+		break;
+	default:
+		return -ENODATA;
+	}
+
+	val = ((((long)word * 1000) >> 9) - TPS40422_VREF + 1) / 2;
+	return pmbus_write_word_data(client, page, reg, val);
+}
+
+
 static struct pmbus_driver_info tps40422_info = {
 	.pages = 2,
+	.read_word_data = tps40422_read_word_data,
+	.write_word_data = tps40422_write_word_data,
 	.format[PSC_VOLTAGE_IN] = linear,
 	.format[PSC_VOLTAGE_OUT] = linear,
 	.format[PSC_TEMPERATURE] = linear,
 	.func[0] = PMBUS_HAVE_VOUT | PMBUS_HAVE_TEMP2
 		| PMBUS_HAVE_STATUS_VOUT | PMBUS_HAVE_STATUS_TEMP
+		| PMBUS_HAVE_VOUT_MARGIN_HIGH | PMBUS_HAVE_VOUT_MARGIN_LOW
 		| PMBUS_HAVE_IOUT | PMBUS_HAVE_STATUS_IOUT,
 	.func[1] = PMBUS_HAVE_VOUT | PMBUS_HAVE_TEMP2
 		| PMBUS_HAVE_STATUS_VOUT | PMBUS_HAVE_STATUS_TEMP
+		| PMBUS_HAVE_VOUT_MARGIN_HIGH | PMBUS_HAVE_VOUT_MARGIN_LOW
 		| PMBUS_HAVE_IOUT | PMBUS_HAVE_STATUS_IOUT,
 };
 
-- 
2.17.1