ALSA: timer: Limit max amount of slave instances

[linux-2.6-block.git] / Documentation / hwmon / adm1021.rst

Kernel driver adm1021
=====================

Supported chips:

  * Analog Devices ADM1021

    Prefix: 'adm1021'

    Addresses scanned: I2C 0x18 - 0x1a, 0x29 - 0x2b, 0x4c - 0x4e

    Datasheet: Publicly available at the Analog Devices website

  * Analog Devices ADM1021A/ADM1023

    Prefix: 'adm1023'

    Addresses scanned: I2C 0x18 - 0x1a, 0x29 - 0x2b, 0x4c - 0x4e

    Datasheet: Publicly available at the Analog Devices website

  * Genesys Logic GL523SM

    Prefix: 'gl523sm'

    Addresses scanned: I2C 0x18 - 0x1a, 0x29 - 0x2b, 0x4c - 0x4e

    Datasheet:

  * Maxim MAX1617

    Prefix: 'max1617'

    Addresses scanned: I2C 0x18 - 0x1a, 0x29 - 0x2b, 0x4c - 0x4e

    Datasheet: Publicly available at the Maxim website

  * Maxim MAX1617A

    Prefix: 'max1617a'

    Addresses scanned: I2C 0x18 - 0x1a, 0x29 - 0x2b, 0x4c - 0x4e

    Datasheet: Publicly available at the Maxim website

  * National Semiconductor LM84

    Prefix: 'lm84'

    Addresses scanned: I2C 0x18 - 0x1a, 0x29 - 0x2b, 0x4c - 0x4e

    Datasheet: Publicly available at the National Semiconductor website

  * Philips NE1617

    Prefix: 'max1617' (probably detected as a max1617)

    Addresses scanned: I2C 0x18 - 0x1a, 0x29 - 0x2b, 0x4c - 0x4e

    Datasheet: Publicly available at the Philips website

  * Philips NE1617A

    Prefix: 'max1617' (probably detected as a max1617)

    Addresses scanned: I2C 0x18 - 0x1a, 0x29 - 0x2b, 0x4c - 0x4e

    Datasheet: Publicly available at the Philips website

  * TI THMC10

    Prefix: 'thmc10'

    Addresses scanned: I2C 0x18 - 0x1a, 0x29 - 0x2b, 0x4c - 0x4e

    Datasheet: Publicly available at the TI website

  * Onsemi MC1066

    Prefix: 'mc1066'

    Addresses scanned: I2C 0x18 - 0x1a, 0x29 - 0x2b, 0x4c - 0x4e

    Datasheet: Publicly available at the Onsemi website


Authors:
	- Frodo Looijaard <frodol@dds.nl>,
	- Philip Edelbrock <phil@netroedge.com>

Module Parameters
-----------------

* read_only: int
  Don't set any values, read only mode


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

The chips supported by this driver are very similar. The Maxim MAX1617 is
the oldest; it has the problem that it is not very well detectable. The
MAX1617A solves that. The ADM1021 is a straight clone of the MAX1617A.
Ditto for the THMC10. From here on, we will refer to all these chips as
ADM1021-clones.

The ADM1021 and MAX1617A reports a die code, which is a sort of revision
code. This can help us pinpoint problems; it is not very useful
otherwise.

ADM1021-clones implement two temperature sensors. One of them is internal,
and measures the temperature of the chip itself; the other is external and
is realised in the form of a transistor-like device. A special alarm
indicates whether the remote sensor is connected.

Each sensor has its own low and high limits. When they are crossed, the
corresponding alarm is set and remains on as long as the temperature stays
out of range. Temperatures are measured in degrees Celsius. Measurements
are possible between -65 and +127 degrees, with a resolution of one degree.

If an alarm triggers, it will remain triggered until the hardware register
is read at least once. This means that the cause for the alarm may already
have disappeared!

This driver only updates its values each 1.5 seconds; reading it more often
will do no harm, but will return 'old' values. It is possible to make
ADM1021-clones do faster measurements, but there is really no good reason
for that.


Netburst-based Xeon support
---------------------------

Some Xeon processors based on the Netburst (early Pentium 4, from 2001 to
2003) microarchitecture had real MAX1617, ADM1021, or compatible chips
within them, with two temperature sensors. Other Xeon processors of this
era (with 400 MHz FSB) had chips with only one temperature sensor.

If you have such an old Xeon, and you get two valid temperatures when
loading the adm1021 module, then things are good.

If nothing happens when loading the adm1021 module, and you are certain
that your specific Xeon processor model includes compatible sensors, you
will have to explicitly instantiate the sensor chips from user-space. See
method 4 in Documentation/i2c/instantiating-devices.rst. Possible slave
addresses are 0x18, 0x1a, 0x29, 0x2b, 0x4c, or 0x4e. It is likely that
only temp2 will be correct and temp1 will have to be ignored.

Previous generations of the Xeon processor (based on Pentium II/III)
didn't have these sensors. Next generations of Xeon processors (533 MHz
FSB and faster) lost them, until the Core-based generation which
introduced integrated digital thermal sensors. These are supported by
the coretemp driver.