hwmon: (lm90) Add explicit support for MAX6648/MAX6692

Unlike MAX6646/MAX6647/MAX6649, MAX6648 and MAX6692 only support
a temperature range of 0..127 degrees C. Separate support for the
two sets of chips to be able to support maximum temperature ranges
correctly for all chips. Introduce new feature flag to indicate
temperature support up to 255 degrees C.

Since the chips are almost identical except for the supported temperature
range, automatic chip detection is limited. Effectively this means that
MAX6648 may be mis-detected as MAX6649 when auto-detected, but there is
nothing we can do about that.

Devicetree nodes are not added for the added chips since it is quite
unlikely that such old chips will ever be used in a devicetree based
system. They can be added later if needed.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/lm90.rst

@@ -105,7 +105,7 @@ Supported chips:
 
   * Maxim MAX6648
 
-    Prefix: 'max6646'
+    Prefix: 'max6648'
 
     Addresses scanned: I2C 0x4c
 
@@ -191,7 +191,7 @@ Supported chips:
 
   * Maxim MAX6692
 
-    Prefix: 'max6646'
+    Prefix: 'max6648'
 
     Addresses scanned: I2C 0x4c
 
@@ -324,6 +324,14 @@ ADT7461, ADT7461A, NCT1008:
   * Lower resolution for remote temperature
   * SMBus PEC support for Write Byte and Receive Byte transactions.
 
+MAX6646, MAX6647, MAX6649:
+  * Better local resolution
+  * Extended range unsigned external temperature
+
+MAX6648, MAX6692:
+  * Better local resolution
+  * Unsigned temperature
+
 MAX6654:
   * Better local resolution
   * Selectable address

drivers/hwmon/lm90.c

@@ -115,7 +115,7 @@ static const unsigned short normal_i2c[] = {
 	0x4d, 0x4e, 0x4f, I2C_CLIENT_END };
 
 enum chips { adm1032, adt7461, adt7461a, g781, lm86, lm90, lm99,
-	max6646, max6654, max6657, max6659, max6680, max6696,
+	max6646, max6648, max6654, max6657, max6659, max6680, max6696,
 	sa56004, tmp451, tmp461, w83l771,
 };
 
@@ -179,6 +179,7 @@ enum chips { adm1032, adt7461, adt7461a, g781, lm86, lm90, lm99,
 #define LM90_HAVE_PEC		BIT(11)	/* Chip supports PEC		*/
 #define LM90_HAVE_PARTIAL_PEC	BIT(12)	/* Partial PEC support (adm1032)*/
 #define LM90_HAVE_ALARMS	BIT(13)	/* Create 'alarms' attribute	*/
+#define LM90_HAVE_EXT_UNSIGNED	BIT(14)	/* extended unsigned temperature*/
 
 /* LM90 status */
 #define LM90_STATUS_LTHRM	BIT(0)	/* local THERM limit tripped */
@@ -213,6 +214,7 @@ static const struct i2c_device_id lm90_id[] = {
 	{ "lm99", lm99 },
 	{ "max6646", max6646 },
 	{ "max6647", max6646 },
+	{ "max6648", max6648 },
 	{ "max6649", max6646 },
 	{ "max6654", max6654 },
 	{ "max6657", max6657 },
@@ -220,6 +222,7 @@ static const struct i2c_device_id lm90_id[] = {
 	{ "max6659", max6659 },
 	{ "max6680", max6680 },
 	{ "max6681", max6680 },
+	{ "max6692", max6648 },
 	{ "max6695", max6696 },
 	{ "max6696", max6696 },
 	{ "nct1008", adt7461a },
@@ -400,7 +403,14 @@ static const struct lm90_params lm90_params[] = {
 	},
 	[max6646] = {
 		.flags = LM90_HAVE_CRIT | LM90_HAVE_BROKEN_ALERT
-		  | LM90_HAVE_UNSIGNED_TEMP | LM90_HAVE_ALARMS,
+		  | LM90_HAVE_EXT_UNSIGNED | LM90_HAVE_ALARMS,
+		.alert_alarms = 0x7c,
+		.max_convrate = 6,
+		.reg_local_ext = MAX6657_REG_LOCAL_TEMPL,
+	},
+	[max6648] = {
+		.flags = LM90_HAVE_UNSIGNED_TEMP | LM90_HAVE_CRIT
+		  | LM90_HAVE_BROKEN_ALERT,
 		.alert_alarms = 0x7c,
 		.max_convrate = 6,
 		.reg_local_ext = MAX6657_REG_LOCAL_TEMPL,
@@ -1119,7 +1129,7 @@ static int lm90_temp_from_reg(u32 flags, u16 regval, u8 resolution)
 
 	if (flags & LM90_HAVE_EXTENDED_TEMP)
 		val = regval - 0x4000;
-	else if (flags & LM90_HAVE_UNSIGNED_TEMP)
+	else if (flags & (LM90_HAVE_UNSIGNED_TEMP | LM90_HAVE_EXT_UNSIGNED))
 		val = regval;
 	else
 		val = (s16)regval;
@@ -1147,6 +1157,8 @@ static u16 lm90_temp_to_reg(u32 flags, long val, u8 resolution)
 	if (flags & LM90_HAVE_EXTENDED_TEMP) {
 		val = clamp_val(val, -64000, 191000 + fraction);
 		val += 64000;
+	} else if (flags & LM90_HAVE_EXT_UNSIGNED) {
+		val = clamp_val(val, 0, 255000 + fraction);
 	} else if (flags & LM90_HAVE_UNSIGNED_TEMP) {
 		val = clamp_val(val, 0, 127000 + fraction);
 	} else {
@@ -1675,10 +1687,31 @@ static const char *lm90_detect_maxim(struct i2c_client *client, int chip_id,
 		 * The chip_id register of the MAX6646/6647/6649 holds the
 		 * revision of the chip. The lowest 6 bits of the config1
 		 * register are unused and should return zero when read.
+		 * The I2C address of MAX6648/6692 is fixed at 0x4c.
+		 * MAX6646 is at address 0x4d, MAX6647 is at address 0x4e,
+		 * and MAX6649 is at address 0x4c. A slight difference between
+		 * the two sets of chips is that the remote temperature register
+		 * reports different values if the DXP pin is open or shorted.
+		 * We can use that information to help distinguish between the
+		 * chips. MAX6648 will be mis-detected as MAX6649 if the remote
+		 * diode is connected, but there isn't really anything we can
+		 * do about that.
 		 */
 		if (!(config1 & 0x3f) && convrate <= 0x07) {
+			int temp;
+
 			switch (address) {
 			case 0x4c:
+				/*
+				 * MAX6649 reports an external temperature
+				 * value of 0xff if DXP is open or shorted.
+				 * MAX6648 reports 0x80 in that case.
+				 */
+				temp = i2c_smbus_read_byte_data(client,
+								LM90_REG_REMOTE_TEMPH);
+				if (temp == 0x80)
+					name = "max6648";
+				else
 					name = "max6649";
 				break;
 			case 0x4d: