Documentation/hwmon/emc1812.rst

.. SPDX-License-Identifier: GPL-2.0-or-later

Kernel driver emc1812
=====================

Supported chips:

  * Microchip EMC1812, EMC1813, EMC1814, EMC1815, EMC1833

    Prefix: 'emc1812'

    Datasheets:

	- https://ww1.microchip.com/downloads/aemDocuments/documents/MSLD/ProductDocuments/DataSheets/EMC1812-3-4-5-33-Data-Sheet-DS20005751.pdf

Author:
    Marius Cristea <marius.cristea@microchip.com>


Description
-----------

The Microchip EMC181x/33 chips contain up to 4 remote temperature sensors
and one internal.
- The EMC1812 is a single channel remote temperature sensor.
- The EMC1813 and EMC1833 are dual channel remote temperature sensor. The
remote channels for this selection of devices can support substrate diodes,
discrete diode-connected transistors or CPU/GPU thermal diodes.
- The EMC1814 is a three channel remote temperature sensor that supports
Anti-Parallel Diode (APD) only on one channel. For the channel that does not
support APD functionality, substrate diodes, discrete diode-connected
transistors or CPU/GPU thermal diodes are supported. For the channel that
supports APD, only discrete diode-connected transistors may be implemented.
However, if APD is disabled on the EMC1814, then the channel that supports
APD will be functional with substrate diodes, discrete diode-connected
transistors and CPU/GPU thermal diodes.
- The EMC1815 is a four channel remote temperature sensor.

The EMC1815 and EMC1833 support APD on all channels. When APD is enabled,
the channels support only diode-connected transistors. If APD is disabled,
then the channels will support substrate transistors, discrete diode-connected
transistors and CPU/GPU thermal diodes.

Note: Disabling APD functionality to implement substrate diodes on devices
that support APD eliminates the benefit of APD (two diodes on one channel).

The chips implement three limits for each sensor: low (tempX_min), high
(tempX_max) and critical (tempX_crit). The chips also implement an
hysteresis mechanism which applies to all 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 three 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.
* The hysteresis values can't be set independently. We decided to make
  only tempX_crit_hyst writable, while all other hysteresis attributes
  are read-only. Setting tempX_crit_hyst writes the difference between
  tempX_crit_hyst and tempX_crit into the chip, and the same relative
  hysteresis applies automatically to all other limits.
* The limits should be set before the hysteresis. At power up the device
  starts with 10 degree hysteresis.