hwmon: (lm90) Add support for MAX6642

MAX6642 is a reduced version of LM90 with no low limits and no conversion
rate register. Its alert functionality is broken, similar to many other
chips supported by the lm90 driver.

After this change, the stand-alone max6642 driver is only needed if the
lm90 driver is disabled. Make it dependent on SENSORS_LM90=n to show that
it is not needed if the lm90 driver is enabled.

A devicetree node is not added for this chip since it is quite unlikely
that such an old chip will ever be used in a devicetree based system.
It can be added later if needed.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>

1 files changed, 16 insertions, 0 deletions

diff --git a/Documentation/hwmon/lm90.rst b/Documentation/hwmon/lm90.rst
index 45bc333a1219..313b18f6531d 100644
--- a/Documentation/hwmon/lm90.rst
+++ b/Documentation/hwmon/lm90.rst
@@ -113,6 +113,16 @@ Supported chips:
 
 	       https://www.onsemi.com/PowerSolutions/product.do?id=NCT1008
 
+  * Maxim MAX6642
+
+    Prefix: 'max6642'
+
+    Addresses scanned: I2C 0x48-0x4f
+
+    Datasheet: Publicly available at the Maxim website
+
+	       http://datasheets.maxim-ic.com/en/ds/MAX6642.pdf
+
   * Maxim MAX6646
 
     Prefix: 'max6646'
@@ -362,6 +372,12 @@ ADT7481, ADT7482, ADT7483:
   * Two remote sensors
   * Selectable address (ADT7483)
 
+MAX6642:
+  * No critical limit register
+  * Conversion rate not configurable
+  * Better local resolution (10 bit)
+  * 10 bit external sensor resolution
+
 MAX6646, MAX6647, MAX6649:
   * Better local resolution
   * Extended range unsigned external temperature