hwmon: (pmbus/bpa-rs600) Add workaround for incorrect Pin max

BPD-RS600 modules running firmware v5.70 misreport the MFR_PIN_MAX.
The indicate a maximum of 1640W instead of 700W. Detect the invalid
reading and return a sensible value instead.
Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Link: https://lore.kernel.org/r/20210812014000.26293-3-chris.packham@alliedtelesis.co.nzSigned-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/pmbus/bpa-rs600.c

@@ -65,6 +65,26 @@ static int bpa_rs600_read_vin(struct i2c_client *client)
 	return ret;
 }
 
+/*
+ * Firmware V5.70 incorrectly reports 1640W for MFR_PIN_MAX.
+ * Deal with this by returning a sensible value.
+ */
+static int bpa_rs600_read_pin_max(struct i2c_client *client)
+{
+	int ret;
+
+	ret = pmbus_read_word_data(client, 0, 0xff, PMBUS_MFR_PIN_MAX);
+	if (ret < 0)
+		return ret;
+
+	/* Detect invalid 1640W (linear encoding) */
+	if (ret == 0x0b34)
+		/* Report 700W (linear encoding) */
+		return 0x095e;
+
+	return ret;
+}
+
 static int bpa_rs600_read_word_data(struct i2c_client *client, int page, int phase, int reg)
 {
 	int ret;
@@ -91,6 +111,9 @@ static int bpa_rs600_read_word_data(struct i2c_client *client, int page, int pha
 	case PMBUS_READ_VIN:
 		ret = bpa_rs600_read_vin(client);
 		break;
+	case PMBUS_MFR_PIN_MAX:
+		ret = bpa_rs600_read_pin_max(client);
+		break;
 	default:
 		if (reg >= PMBUS_VIRT_BASE)
 			ret = -ENXIO;