hwmon: (ltc2978) Add missing chip IDs for LTC2978 and LTC3882

Add additional chip ID for an older revision of LTC2978, as well
as two chip IDs for LTC3882. Turns out the LTC3882 does support the
LTC2978_MFR_SPECIAL_ID register, and reading it returns its chip ID,
but the register is undocumented.

Suggested-by: Michael Jones <mike@proclivis.com>
Tested-by: Michael Jones <mike@proclivis.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/pmbus/ltc2978.c

@@ -31,7 +31,7 @@ enum chips { ltc2974, ltc2975, ltc2977, ltc2978, ltc3880, ltc3882, ltc3883,
 #define LTC2978_MFR_VOUT_PEAK		0xdd
 #define LTC2978_MFR_VIN_PEAK		0xde
 #define LTC2978_MFR_TEMPERATURE_PEAK	0xdf
-#define LTC2978_MFR_SPECIAL_ID		0xe7	/* Not on LTC3882 */
+#define LTC2978_MFR_SPECIAL_ID		0xe7	/* Undocumented on LTC3882 */
 
 /* LTC2974, LTC2975, LCT2977, and LTC2978 */
 #define LTC2978_MFR_VOUT_MIN		0xfb
@@ -61,8 +61,11 @@ enum chips { ltc2974, ltc2975, ltc2977, ltc2978, ltc3880, ltc3882, ltc3883,
 #define LTC2974_ID			0x0210
 #define LTC2975_ID			0x0220
 #define LTC2977_ID			0x0130
-#define LTC2978_ID			0x0120
+#define LTC2978_ID_REV1			0x0110	/* Early revision */
+#define LTC2978_ID_REV2			0x0120
 #define LTC3880_ID			0x4020
+#define LTC3882_ID			0x4200
+#define LTC3882_ID_D1			0x4240	/* Dash 1 */
 #define LTC3883_ID			0x4300
 #define LTC3887_ID			0x4700
 #define LTM4676_ID_REV1			0x4400
@@ -466,10 +469,12 @@ static int ltc2978_get_id(struct i2c_client *client)
 		return ltc2975;
 	else if (chip_id == LTC2977_ID)
 		return ltc2977;
-	else if (chip_id == LTC2978_ID)
+	else if (chip_id == LTC2978_ID_REV1 || chip_id == LTC2978_ID_REV2)
 		return ltc2978;
 	else if (chip_id == LTC3880_ID)
 		return ltc3880;
+	else if (chip_id == LTC3882_ID || chip_id == LTC3882_ID_D1)
+		return ltc3882;
 	else if (chip_id == LTC3883_ID)
 		return ltc3883;
 	else if (chip_id == LTC3887_ID)