Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 38 insertions, 0 deletions

diff --git a/Documentation/hwmon/lm77 b/Documentation/hwmon/lm77
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+Kernel driver lm77
+==================
+
+Supported chips:
+  * National Semiconductor LM77
+    Prefix: 'lm77'
+    Addresses scanned: I2C 0x48 - 0x4b
+    Datasheet: Publicly available at the National Semiconductor website
+               http://www.national.com/
+
+Author: Andras BALI <drewie@freemail.hu>
+
+Description
+-----------
+
+The LM77 implements one temperature sensor. The temperature
+sensor incorporates a band-gap type temperature sensor,
+10-bit ADC, and a digital comparator with user-programmable upper
+and lower limit values.
+
+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.