Merge tag 'firewire-updates' of git://git.kernel.org/pub/scm/linux/kernel/git/ieee139...

[karo-tx-linux.git] / Documentation / hwmon / lm77

diff --git a/Documentation/hwmon/lm77 b/Documentation/hwmon/lm77
index 57c3a46d637096c485e31556dba357c2415d1866..bfc915fe3639e83183e283ce8d22cf979747ceb5 100644 (file)
--- a/Documentation/hwmon/lm77
+++ b/Documentation/hwmon/lm77
@@ -18,5 +18,21 @@ sensor incorporates a band-gap type temperature sensor,
 10-bit ADC, and a digital comparator with user-programmable upper
 and lower limit values.
 
-Limits can be set through the Overtemperature Shutdown register and
-Hysteresis register.
+The LM77 implements 3 limits: low (temp1_min), high (temp1_max) and
+critical (temp1_crit.) It also implements an hysteresis mechanism which
+applies to all 3 limits. The relative difference is stored in a single
+register on the chip, which means that the relative difference between
+the limit and its hysteresis is always the same for all 3 limits.
+
+This implementation detail implies the following:
+* When setting a limit, its hysteresis will automatically follow, the
+  difference staying unchanged. For example, if the old critical limit
+  was 80 degrees C, and the hysteresis was 75 degrees C, and you change
+  the critical limit to 90 degrees C, then the hysteresis will
+  automatically change to 85 degrees C.
+* All 3 hysteresis can't be set independently. We decided to make
+  temp1_crit_hyst writable, while temp1_min_hyst and temp1_max_hyst are
+  read-only. Setting temp1_crit_hyst writes the difference between
+  temp1_crit_hyst and temp1_crit into the chip, and the same relative
+  hysteresis applies automatically to the low and high limits.
+* The limits should be set before the hysteresis.