hwmon: (lm75) Tune resolution and sample time per chip

Most LM75-compatible chips can either sample much faster or with a
much better resolution than the original LM75 chip. So far the lm75
driver did not let the user take benefit of these improvements. Do it
now.

I decided to almost always configure the chip to use the best
resolution possible, which also means the longest sample time. The
only chips for which I didn't are the DS75, DS1775 and STDS75, because
they are really too slow in 12-bit mode (1.2 to 1.5 second worst case)
so I went for 11-bit mode as a more reasonable tradeoff. This choice is
dictated by the fact that the hwmon subsystem is meant for system
monitoring, it has never been supposed to be ultra-fast, and as a
matter of fact we do cache the sampled values in almost all drivers.

If anyone isn't pleased with these default settings, they can always
introduce a platform data structure or DT support for the lm75. That
being said, it seems nobody ever complained that the driver wouldn't
refresh the value faster than every 1.5 second, and the change made
it faster for all chips even in 12-bit mode, so I don't expect any
complaint.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Guenter Roeck <linux@roeck-us.net>

1 files changed, 4 insertions, 3 deletions

diff --git a/Documentation/hwmon/lm75 b/Documentation/hwmon/lm75
index 69af1c7..5e45d07 100644
--- a/Documentation/hwmon/lm75
+++ b/Documentation/hwmon/lm75
@@ -67,7 +67,8 @@ the temperature falls below the Hysteresis value.
 All temperatures are in degrees Celsius, and are guaranteed within a
 range of -55 to +125 degrees.
 
-The LM75 only updates its values each 1.5 seconds; reading it more often
+The driver caches the values for a period varying between 1 second for the
+slowest chips and 125 ms for the fastest chips; reading it more often
 will do no harm, but will return 'old' values.
 
 The original LM75 was typically used in combination with LM78-like chips
@@ -78,8 +79,8 @@ The LM75 is essentially an industry standard; there may be other
 LM75 clones not listed here, with or without various enhancements,
 that are supported. The clones are not detected by the driver, unless
 they reproduce the exact register tricks of the original LM75, and must
-therefore be instantiated explicitly. The specific enhancements (such as
-higher resolution) are not currently supported by the driver.
+therefore be instantiated explicitly. Higher resolution up to 12-bit
+is supported by this driver, other specific enhancements are not.
 
 The LM77 is not supported, contrary to what we pretended for a long time.
 Both chips are simply not compatible, value encoding differs.