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-Kernel driver lm90
-==================
-
-Supported chips:
- * National Semiconductor LM90
- Prefix: 'lm90'
- Addresses scanned: I2C 0x4c
- Datasheet: Publicly available at the National Semiconductor website
- http://www.national.com/pf/LM/LM90.html
- * National Semiconductor LM89
- Prefix: 'lm89' (no auto-detection)
- Addresses scanned: I2C 0x4c and 0x4d
- Datasheet: Publicly available at the National Semiconductor website
- http://www.national.com/mpf/LM/LM89.html
- * National Semiconductor LM99
- Prefix: 'lm99'
- Addresses scanned: I2C 0x4c and 0x4d
- Datasheet: Publicly available at the National Semiconductor website
- http://www.national.com/pf/LM/LM99.html
- * National Semiconductor LM86
- Prefix: 'lm86'
- Addresses scanned: I2C 0x4c
- Datasheet: Publicly available at the National Semiconductor website
- http://www.national.com/mpf/LM/LM86.html
- * Analog Devices ADM1032
- Prefix: 'adm1032'
- Addresses scanned: I2C 0x4c and 0x4d
- Datasheet: Publicly available at the ON Semiconductor website
- http://www.onsemi.com/PowerSolutions/product.do?id=ADM1032
- * Analog Devices ADT7461
- Prefix: 'adt7461'
- Addresses scanned: I2C 0x4c and 0x4d
- Datasheet: Publicly available at the ON Semiconductor website
- http://www.onsemi.com/PowerSolutions/product.do?id=ADT7461
- * Analog Devices ADT7461A
- Prefix: 'adt7461a'
- Addresses scanned: I2C 0x4c and 0x4d
- Datasheet: Publicly available at the ON Semiconductor website
- http://www.onsemi.com/PowerSolutions/product.do?id=ADT7461A
- * ON Semiconductor NCT1008
- Prefix: 'nct1008'
- Addresses scanned: I2C 0x4c and 0x4d
- Datasheet: Publicly available at the ON Semiconductor website
- http://www.onsemi.com/PowerSolutions/product.do?id=NCT1008
- * Maxim MAX6646
- Prefix: 'max6646'
- Addresses scanned: I2C 0x4d
- Datasheet: Publicly available at the Maxim website
- http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
- * Maxim MAX6647
- Prefix: 'max6646'
- Addresses scanned: I2C 0x4e
- Datasheet: Publicly available at the Maxim website
- http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
- * Maxim MAX6648
- Prefix: 'max6646'
- Addresses scanned: I2C 0x4c
- Datasheet: Publicly available at the Maxim website
- http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3500
- * Maxim MAX6649
- Prefix: 'max6646'
- Addresses scanned: I2C 0x4c
- Datasheet: Publicly available at the Maxim website
- http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497
- * Maxim MAX6657
- Prefix: 'max6657'
- Addresses scanned: I2C 0x4c
- Datasheet: Publicly available at the Maxim website
- http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
- * Maxim MAX6658
- Prefix: 'max6657'
- Addresses scanned: I2C 0x4c
- Datasheet: Publicly available at the Maxim website
- http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
- * Maxim MAX6659
- Prefix: 'max6659'
- Addresses scanned: I2C 0x4c, 0x4d, 0x4e
- Datasheet: Publicly available at the Maxim website
- http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578
- * Maxim MAX6680
- Prefix: 'max6680'
- Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
- 0x4c, 0x4d and 0x4e
- Datasheet: Publicly available at the Maxim website
- http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370
- * Maxim MAX6681
- Prefix: 'max6680'
- Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
- 0x4c, 0x4d and 0x4e
- Datasheet: Publicly available at the Maxim website
- http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3370
- * Maxim MAX6692
- Prefix: 'max6646'
- Addresses scanned: I2C 0x4c
- Datasheet: Publicly available at the Maxim website
- http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3500
- * Maxim MAX6695
- Prefix: 'max6695'
- Addresses scanned: I2C 0x18
- Datasheet: Publicly available at the Maxim website
- http://www.maxim-ic.com/datasheet/index.mvp/id/4199
- * Maxim MAX6696
- Prefix: 'max6695'
- Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b,
- 0x4c, 0x4d and 0x4e
- Datasheet: Publicly available at the Maxim website
- http://www.maxim-ic.com/datasheet/index.mvp/id/4199
- * Winbond/Nuvoton W83L771W/G
- Prefix: 'w83l771'
- Addresses scanned: I2C 0x4c
- Datasheet: No longer available
- * Winbond/Nuvoton W83L771AWG/ASG
- Prefix: 'w83l771'
- Addresses scanned: I2C 0x4c
- Datasheet: Not publicly available, can be requested from Nuvoton
- * Philips/NXP SA56004X
- Prefix: 'sa56004'
- Addresses scanned: I2C 0x48 through 0x4F
- Datasheet: Publicly available at NXP website
- http://ics.nxp.com/products/interface/datasheet/sa56004x.pdf
- * GMT G781
- Prefix: 'g781'
- Addresses scanned: I2C 0x4c, 0x4d
- Datasheet: Not publicly available from GMT
-
-Author: Jean Delvare <khali@linux-fr.org>
-
-
-Description
------------
-
-The LM90 is a digital temperature sensor. It senses its own temperature as
-well as the temperature of up to one external diode. It is compatible
-with many other devices, many of which are supported by this driver.
-
-Note that there is no easy way to differentiate between the MAX6657,
-MAX6658 and MAX6659 variants. The extra features of the MAX6659 are only
-supported by this driver if the chip is located at address 0x4d or 0x4e,
-or if the chip type is explicitly selected as max6659.
-The MAX6680 and MAX6681 only differ in their pinout, therefore they obviously
-can't (and don't need to) be distinguished.
-
-The specificity of this family of chipsets over the ADM1021/LM84
-family is that it features critical limits with hysteresis, and an
-increased resolution of the remote temperature measurement.
-
-The different chipsets of the family are not strictly identical, although
-very similar. For reference, here comes a non-exhaustive list of specific
-features:
-
-LM90:
- * Filter and alert configuration register at 0xBF.
- * ALERT is triggered by temperatures over critical limits.
-
-LM86 and LM89:
- * Same as LM90
- * Better external channel accuracy
-
-LM99:
- * Same as LM89
- * External temperature shifted by 16 degrees down
-
-ADM1032:
- * Consecutive alert register at 0x22.
- * Conversion averaging.
- * Up to 64 conversions/s.
- * ALERT is triggered by open remote sensor.
- * SMBus PEC support for Write Byte and Receive Byte transactions.
-
-ADT7461, ADT7461A, NCT1008:
- * Extended temperature range (breaks compatibility)
- * Lower resolution for remote temperature
-
-MAX6657 and MAX6658:
- * Better local resolution
- * Remote sensor type selection
-
-MAX6659:
- * Better local resolution
- * Selectable address
- * Second critical temperature limit
- * Remote sensor type selection
-
-MAX6680 and MAX6681:
- * Selectable address
- * Remote sensor type selection
-
-MAX6695 and MAX6696:
- * Better local resolution
- * Selectable address (max6696)
- * Second critical temperature limit
- * Two remote sensors
-
-W83L771W/G
- * The G variant is lead-free, otherwise similar to the W.
- * Filter and alert configuration register at 0xBF
- * Moving average (depending on conversion rate)
-
-W83L771AWG/ASG
- * Successor of the W83L771W/G, same features.
- * The AWG and ASG variants only differ in package format.
- * Diode ideality factor configuration (remote sensor) at 0xE3
-
-SA56004X:
- * Better local resolution
-
-All temperature values are given in degrees Celsius. Resolution
-is 1.0 degree for the local temperature, 0.125 degree for the remote
-temperature, except for the MAX6657, MAX6658 and MAX6659 which have a
-resolution of 0.125 degree for both temperatures.
-
-Each sensor has its own high and low limits, plus a critical limit.
-Additionally, there is a relative hysteresis value common to both critical
-values. To make life easier to user-space applications, two absolute values
-are exported, one for each channel, but these values are of course linked.
-Only the local hysteresis can be set from user-space, and the same delta
-applies to the remote hysteresis.
-
-The lm90 driver will not update its values more frequently than configured with
-the update_interval attribute; reading them more often will do no harm, but will
-return 'old' values.
-
-SMBus Alert Support
--------------------
-
-This driver has basic support for SMBus alert. When an alert is received,
-the status register is read and the faulty temperature channel is logged.
-
-The Analog Devices chips (ADM1032, ADT7461 and ADT7461A) and ON
-Semiconductor chips (NCT1008) do not implement the SMBus alert protocol
-properly so additional care is needed: the ALERT output is disabled when
-an alert is received, and is re-enabled only when the alarm is gone.
-Otherwise the chip would block alerts from other chips in the bus as long
-as the alarm is active.
-
-PEC Support
------------
-
-The ADM1032 is the only chip of the family which supports PEC. It does
-not support PEC on all transactions though, so some care must be taken.
-
-When reading a register value, the PEC byte is computed and sent by the
-ADM1032 chip. However, in the case of a combined transaction (SMBus Read
-Byte), the ADM1032 computes the CRC value over only the second half of
-the message rather than its entirety, because it thinks the first half
-of the message belongs to a different transaction. As a result, the CRC
-value differs from what the SMBus master expects, and all reads fail.
-
-For this reason, the lm90 driver will enable PEC for the ADM1032 only if
-the bus supports the SMBus Send Byte and Receive Byte transaction types.
-These transactions will be used to read register values, instead of
-SMBus Read Byte, and PEC will work properly.
-
-Additionally, the ADM1032 doesn't support SMBus Send Byte with PEC.
-Instead, it will try to write the PEC value to the register (because the
-SMBus Send Byte transaction with PEC is similar to a Write Byte transaction
-without PEC), which is not what we want. Thus, PEC is explicitly disabled
-on SMBus Send Byte transactions in the lm90 driver.
-
-PEC on byte data transactions represents a significant increase in bandwidth
-usage (+33% for writes, +25% for reads) in normal conditions. With the need
-to use two SMBus transaction for reads, this overhead jumps to +50%. Worse,
-two transactions will typically mean twice as much delay waiting for
-transaction completion, effectively doubling the register cache refresh time.
-I guess reliability comes at a price, but it's quite expensive this time.
-
-So, as not everyone might enjoy the slowdown, PEC can be disabled through
-sysfs. Just write 0 to the "pec" file and PEC will be disabled. Write 1
-to that file to enable PEC again.