| Kernel driver lm90 | 
 | ================== | 
 |  | 
 | Supported chips: | 
 |  | 
 |   * National Semiconductor LM84 | 
 |  | 
 |     Prefix: 'lm84' | 
 |  | 
 |     Addresses scanned: I2C 0x18 - 0x1a, 0x29 - 0x2b, 0x4c - 0x4e | 
 |  | 
 |     Datasheet: Publicly available at the National Semiconductor website | 
 |  | 
 |   * 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 ADM1020 | 
 |  | 
 |     Prefix: 'adm1020' | 
 |  | 
 |     Addresses scanned: I2C 0x4c - 0x4e | 
 |  | 
 |     Datasheet: Publicly available at the Analog Devices website | 
 |  | 
 |   * 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 | 
 |  | 
 |   * Analog Devices ADM1032 | 
 |  | 
 |     Prefix: 'adm1032' | 
 |  | 
 |     Addresses scanned: I2C 0x4c and 0x4d | 
 |  | 
 |     Datasheet: Publicly available at the ON Semiconductor website | 
 |  | 
 | 	       https://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 | 
 |  | 
 | 	       https://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 | 
 |  | 
 | 	       https://www.onsemi.com/PowerSolutions/product.do?id=ADT7461A | 
 |  | 
 |   * Analog Devices ADT7481 | 
 |  | 
 |     Prefix: 'adt7481' | 
 |  | 
 |     Addresses scanned: I2C 0x4b and 0x4c | 
 |  | 
 |     Datasheet: Publicly available at the ON Semiconductor website | 
 |  | 
 | 	       https://www.onsemi.com/PowerSolutions/product.do?id=ADT7481 | 
 |  | 
 |   * Analog Devices ADT7482 | 
 |  | 
 |     Prefix: 'adt7482' | 
 |  | 
 |     Addresses scanned: I2C 0x4c | 
 |  | 
 |     Datasheet: Publicly available at the ON Semiconductor website | 
 |  | 
 | 	       https://www.onsemi.com/PowerSolutions/product.do?id=ADT7482 | 
 |  | 
 |   * Analog Devices ADT7483A | 
 |  | 
 |     Prefix: 'adt7483a' | 
 |  | 
 |     Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b, 0x4c, 0x4d, 0x4e | 
 |  | 
 |     Datasheet: Publicly available at the ON Semiconductor website | 
 |  | 
 | 	       https://www.onsemi.com/PowerSolutions/product.do?id=ADT7483A | 
 |  | 
 |   * ON Semiconductor NCT1008 | 
 |  | 
 |     Prefix: 'nct1008' | 
 |  | 
 |     Addresses scanned: I2C 0x4c and 0x4d | 
 |  | 
 |     Datasheet: Publicly available at the ON Semiconductor website | 
 |  | 
 | 	       https://www.onsemi.com/PowerSolutions/product.do?id=NCT1008 | 
 |  | 
 |   * ON Semiconductor NCT210 | 
 |  | 
 |     Prefix: 'adm1021' | 
 |  | 
 |     Addresses scanned: I2C 0x18 - 0x1a, 0x29 - 0x2b, 0x4c - 0x4e | 
 |  | 
 |     Datasheet: Publicly available at the ON Semiconductor website | 
 |  | 
 | 	       https://www.onsemi.com/PowerSolutions/product.do?id=NCT210 | 
 |  | 
 |   * ON Semiconductor NCT214 | 
 |  | 
 |     Prefix: 'nct214' | 
 |  | 
 |     Addresses scanned: I2C 0x18 - 0x1a, 0x29 - 0x2b, 0x4c - 0x4e | 
 |  | 
 |     Datasheet: Publicly available at the ON Semiconductor website | 
 |  | 
 | 	       https://www.onsemi.com/PowerSolutions/product.do?id=NCT214 | 
 |  | 
 |   * ON Semiconductor NCT218 | 
 |  | 
 |     Prefix: 'nct218' | 
 |  | 
 |     Addresses scanned: I2C 0x4c - 0x4d | 
 |  | 
 |     Datasheet: Publicly available at the ON Semiconductor website | 
 |  | 
 | 	       https://www.onsemi.com/PowerSolutions/product.do?id=NCT218 | 
 |  | 
 |   * ON Semiconductor NCT72 | 
 |  | 
 |     Prefix: 'nct72' | 
 |  | 
 |     Addresses scanned: I2C 0x4c - 0x4d | 
 |  | 
 |     Datasheet: Publicly available at the ON Semiconductor website | 
 |  | 
 | 	       https://www.onsemi.com/PowerSolutions/product.do?id=NCT72 | 
 |  | 
 |   * 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 | 
 |  | 
 |   * Maxim MAX6642 | 
 |  | 
 |     Prefix: 'max6642' | 
 |  | 
 |     Addresses scanned: I2C 0x48-0x4f | 
 |  | 
 |     Datasheet: Publicly available at the Maxim website | 
 |  | 
 | 	       http://datasheets.maxim-ic.com/en/ds/MAX6642.pdf | 
 |  | 
 |   * 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: 'max6648' | 
 |  | 
 |     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 MAX6654 | 
 |  | 
 |     Prefix: 'max6654' | 
 |  | 
 |     Addresses scanned: I2C 0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b, | 
 |  | 
 | 			   0x4c, 0x4d and 0x4e | 
 |  | 
 |     Datasheet: Publicly available at the Maxim website | 
 |  | 
 | 	       https://www.maximintegrated.com/en/products/sensors/MAX6654.html | 
 |  | 
 |   * 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: 'max6648' | 
 |  | 
 |     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 | 
 |  | 
 |   * Nuvoton NCT7716 | 
 |  | 
 |     Prefix: 'nct7716' | 
 |  | 
 |     Addresses scanned: I2C 0x48, 0x49 | 
 |  | 
 |     Datasheet: Not publicly available, can be requested from Nuvoton | 
 |  | 
 |   * Nuvoton NCT7717 | 
 |  | 
 |     Prefix: 'nct7717' | 
 |  | 
 |     Addresses scanned: I2C 0x48 | 
 |  | 
 |     Datasheet: Publicly available at Nuvoton website | 
 |  | 
 |                https://www.nuvoton.com/resource-files/Nuvoton_NCT7717U_Datasheet_V111.pdf | 
 |  | 
 |   * Nuvoton NCT7718 | 
 |  | 
 |     Prefix: 'nct7718' | 
 |  | 
 |     Addresses scanned: I2C 0x4c | 
 |  | 
 |     Datasheet: Publicly available at Nuvoton website | 
 |  | 
 |                https://www.nuvoton.com/resource-files/Nuvoton_NCT7718W_Datasheet_V11.pdf | 
 |  | 
 |   * 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 | 
 |  | 
 |   * Texas Instruments TMP451 | 
 |  | 
 |     Prefix: 'tmp451' | 
 |  | 
 |     Addresses scanned: I2C 0x4c | 
 |  | 
 |     Datasheet: Publicly available at TI website | 
 |  | 
 | 	       https://www.ti.com/litv/pdf/sbos686 | 
 |  | 
 |   * Texas Instruments TMP461 | 
 |  | 
 |     Prefix: 'tmp461' | 
 |  | 
 |     Addresses scanned: I2C 0x48 through 0x4F | 
 |  | 
 |     Datasheet: Publicly available at TI website | 
 |  | 
 | 	       https://www.ti.com/lit/gpn/tmp461 | 
 |  | 
 |   * Philips NE1617, NE1617A | 
 |  | 
 |     Prefix: 'max1617' (probably detected as a max1617) | 
 |  | 
 |     Addresses scanned: I2C 0x18 - 0x1a, 0x29 - 0x2b, 0x4c - 0x4e | 
 |  | 
 |     Datasheets: Publicly available at the Philips website | 
 |  | 
 |   * Philips NE1618 | 
 |  | 
 |     Prefix: 'ne1618' | 
 |  | 
 |     Addresses scanned: I2C 0x18 - 0x1a, 0x29 - 0x2b, 0x4c - 0x4e | 
 |  | 
 |     Datasheets: Publicly available at the Philips website | 
 |  | 
 |   * Genesys Logic GL523SM | 
 |  | 
 |     Prefix: 'gl523sm' | 
 |  | 
 |     Addresses scanned: I2C 0x18 - 0x1a, 0x29 - 0x2b, 0x4c - 0x4e | 
 |  | 
 |     Datasheet: | 
 |  | 
 |   * 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 | 
 |  | 
 | Author: Jean Delvare <jdelvare@suse.de> | 
 |  | 
 |  | 
 | 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. | 
 |  | 
 | The family of chips supported by this driver is derived from MAX1617. | 
 | This chip as well as various compatible chips support a local and a remote | 
 | temperature sensor with 8 bit accuracy. Later chips provide improved accuracy | 
 | and other additional features such as hysteresis and temperature offset | 
 | registers. | 
 |  | 
 | 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 different chipsets of the family are not strictly identical, although | 
 | very similar. For reference, here comes a non-exhaustive list of specific | 
 | features: | 
 |  | 
 | LM84: | 
 |   * 8 bit sensor resolution | 
 |  | 
 | ADM1020, ADM1021, GL523SM, MAX1617, NE1617, NE1617A, THMC10: | 
 |   * 8 bit sensor resolution | 
 |   * Low temperature limits | 
 |  | 
 | NCT210, NE1618: | 
 |   * 11 bit sensor resolution for remote temperature sensor | 
 |   * Low temperature limits | 
 |  | 
 | ADM1021A, ADM1023: | 
 |   * Temperature offset register for remote temperature sensor | 
 |   * 11 bit resolution for remote temperature sensor | 
 |   * Low temperature limits | 
 |  | 
 | LM90: | 
 |   * 11 bit resolution for remote temperature sensor | 
 |   * Temperature offset register for remote temperature sensor | 
 |   * Low and critical temperature limits | 
 |   * Configurable conversion rate | 
 |   * 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 | 
 |   * SMBus PEC support for Write Byte and Receive Byte transactions. | 
 |   * 10 bit temperature resolution | 
 |  | 
 | ADT7481, ADT7482, ADT7483: | 
 |   * Temperature offset register | 
 |   * SMBus PEC support | 
 |   * 10 bit temperature resolution for external sensors | 
 |   * Two remote sensors | 
 |   * Selectable address (ADT7483) | 
 |  | 
 | MAX6642: | 
 |   * No critical limit register | 
 |   * Conversion rate not configurable | 
 |   * Better local resolution (10 bit) | 
 |   * 10 bit external sensor resolution | 
 |  | 
 | MAX6646, MAX6647, MAX6649: | 
 |   * Better local resolution | 
 |   * Extended range unsigned external temperature | 
 |  | 
 | MAX6648, MAX6692: | 
 |   * Better local resolution | 
 |   * Unsigned temperature | 
 |  | 
 | MAX6654, MAX6690: | 
 |   * Better local resolution | 
 |   * Selectable address | 
 |   * Remote sensor type selection | 
 |   * Extended temperature range | 
 |   * Extended resolution only available when conversion rate <= 1 Hz | 
 |  | 
 | 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 | 
 |  | 
 | NCT7716: | 
 |   * 8 bit sensor resolution | 
 |   * Selectable address | 
 |   * Configurable conversion rate | 
 |  | 
 | NCT7717: | 
 |   * 8 bit sensor resolution | 
 |   * Configurable conversion rate | 
 |  | 
 | NCT7718: | 
 |   * Temperature offset register for remote temperature sensor | 
 |   * 11 bit resolution for remote temperature sensor | 
 |   * Low temperature limits | 
 |   * Configurable conversion rate | 
 |  | 
 | 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 MAX6654, 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 is disabled by default and | 
 | can be enabled through sysfs. Just write 1 to the "pec" file and PEC will be | 
 | enabled. Write 0 to that file to disable PEC again. |