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diff --git a/Documentation/hwmon/pmbus-core b/Documentation/hwmon/pmbus-core deleted file mode 100644 index 8ed10e9ddfb5..000000000000 --- a/Documentation/hwmon/pmbus-core +++ /dev/null @@ -1,283 +0,0 @@ -PMBus core driver and internal API -================================== - -Introduction -============ - -[from pmbus.org] The Power Management Bus (PMBus) is an open standard -power-management protocol with a fully defined command language that facilitates -communication with power converters and other devices in a power system. The -protocol is implemented over the industry-standard SMBus serial interface and -enables programming, control, and real-time monitoring of compliant power -conversion products. This flexible and highly versatile standard allows for -communication between devices based on both analog and digital technologies, and -provides true interoperability which will reduce design complexity and shorten -time to market for power system designers. Pioneered by leading power supply and -semiconductor companies, this open power system standard is maintained and -promoted by the PMBus Implementers Forum (PMBus-IF), comprising 30+ adopters -with the objective to provide support to, and facilitate adoption among, users. - -Unfortunately, while PMBus commands are standardized, there are no mandatory -commands, and manufacturers can add as many non-standard commands as they like. -Also, different PMBUs devices act differently if non-supported commands are -executed. Some devices return an error, some devices return 0xff or 0xffff and -set a status error flag, and some devices may simply hang up. - -Despite all those difficulties, a generic PMBus device driver is still useful -and supported since kernel version 2.6.39. However, it was necessary to support -device specific extensions in addition to the core PMBus driver, since it is -simply unknown what new device specific functionality PMBus device developers -come up with next. - -To make device specific extensions as scalable as possible, and to avoid having -to modify the core PMBus driver repeatedly for new devices, the PMBus driver was -split into core, generic, and device specific code. The core code (in -pmbus_core.c) provides generic functionality. The generic code (in pmbus.c) -provides support for generic PMBus devices. Device specific code is responsible -for device specific initialization and, if needed, maps device specific -functionality into generic functionality. This is to some degree comparable -to PCI code, where generic code is augmented as needed with quirks for all kinds -of devices. - -PMBus device capabilities auto-detection -======================================== - -For generic PMBus devices, code in pmbus.c attempts to auto-detect all supported -PMBus commands. Auto-detection is somewhat limited, since there are simply too -many variables to consider. For example, it is almost impossible to autodetect -which PMBus commands are paged and which commands are replicated across all -pages (see the PMBus specification for details on multi-page PMBus devices). - -For this reason, it often makes sense to provide a device specific driver if not -all commands can be auto-detected. The data structures in this driver can be -used to inform the core driver about functionality supported by individual -chips. - -Some commands are always auto-detected. This applies to all limit commands -(lcrit, min, max, and crit attributes) as well as associated alarm attributes. -Limits and alarm attributes are auto-detected because there are simply too many -possible combinations to provide a manual configuration interface. - -PMBus internal API -================== - -The API between core and device specific PMBus code is defined in -drivers/hwmon/pmbus/pmbus.h. In addition to the internal API, pmbus.h defines -standard PMBus commands and virtual PMBus commands. - -Standard PMBus commands ------------------------ - -Standard PMBus commands (commands values 0x00 to 0xff) are defined in the PMBUs -specification. - -Virtual PMBus commands ----------------------- - -Virtual PMBus commands are provided to enable support for non-standard -functionality which has been implemented by several chip vendors and is thus -desirable to support. - -Virtual PMBus commands start with command value 0x100 and can thus easily be -distinguished from standard PMBus commands (which can not have values larger -than 0xff). Support for virtual PMBus commands is device specific and thus has -to be implemented in device specific code. - -Virtual commands are named PMBUS_VIRT_xxx and start with PMBUS_VIRT_BASE. All -virtual commands are word sized. - -There are currently two types of virtual commands. - -- READ commands are read-only; writes are either ignored or return an error. -- RESET commands are read/write. Reading reset registers returns zero - (used for detection), writing any value causes the associated history to be - reset. - -Virtual commands have to be handled in device specific driver code. Chip driver -code returns non-negative values if a virtual command is supported, or a -negative error code if not. The chip driver may return -ENODATA or any other -Linux error code in this case, though an error code other than -ENODATA is -handled more efficiently and thus preferred. Either case, the calling PMBus -core code will abort if the chip driver returns an error code when reading -or writing virtual registers (in other words, the PMBus core code will never -send a virtual command to a chip). - -PMBus driver information ------------------------- - -PMBus driver information, defined in struct pmbus_driver_info, is the main means -for device specific drivers to pass information to the core PMBus driver. -Specifically, it provides the following information. - -- For devices supporting its data in Direct Data Format, it provides coefficients - for converting register values into normalized data. This data is usually - provided by chip manufacturers in device datasheets. -- Supported chip functionality can be provided to the core driver. This may be - necessary for chips which react badly if non-supported commands are executed, - and/or to speed up device detection and initialization. -- Several function entry points are provided to support overriding and/or - augmenting generic command execution. This functionality can be used to map - non-standard PMBus commands to standard commands, or to augment standard - command return values with device specific information. - - API functions - ------------- - - Functions provided by chip driver - --------------------------------- - - All functions return the command return value (read) or zero (write) if - successful. A return value of -ENODATA indicates that there is no manufacturer - specific command, but that a standard PMBus command may exist. Any other - negative return value indicates that the commands does not exist for this - chip, and that no attempt should be made to read or write the standard - command. - - As mentioned above, an exception to this rule applies to virtual commands, - which _must_ be handled in driver specific code. See "Virtual PMBus Commands" - above for more details. - - Command execution in the core PMBus driver code is as follows. - - if (chip_access_function) { - status = chip_access_function(); - if (status != -ENODATA) - return status; - } - if (command >= PMBUS_VIRT_BASE) /* For word commands/registers only */ - return -EINVAL; - return generic_access(); - - Chip drivers may provide pointers to the following functions in struct - pmbus_driver_info. All functions are optional. - - int (*read_byte_data)(struct i2c_client *client, int page, int reg); - - Read byte from page <page>, register <reg>. - <page> may be -1, which means "current page". - - int (*read_word_data)(struct i2c_client *client, int page, int reg); - - Read word from page <page>, register <reg>. - - int (*write_word_data)(struct i2c_client *client, int page, int reg, - u16 word); - - Write word to page <page>, register <reg>. - - int (*write_byte)(struct i2c_client *client, int page, u8 value); - - Write byte to page <page>, register <reg>. - <page> may be -1, which means "current page". - - int (*identify)(struct i2c_client *client, struct pmbus_driver_info *info); - - Determine supported PMBus functionality. This function is only necessary - if a chip driver supports multiple chips, and the chip functionality is not - pre-determined. It is currently only used by the generic pmbus driver - (pmbus.c). - - Functions exported by core driver - --------------------------------- - - Chip drivers are expected to use the following functions to read or write - PMBus registers. Chip drivers may also use direct I2C commands. If direct I2C - commands are used, the chip driver code must not directly modify the current - page, since the selected page is cached in the core driver and the core driver - will assume that it is selected. Using pmbus_set_page() to select a new page - is mandatory. - - int pmbus_set_page(struct i2c_client *client, u8 page); - - Set PMBus page register to <page> for subsequent commands. - - int pmbus_read_word_data(struct i2c_client *client, u8 page, u8 reg); - - Read word data from <page>, <reg>. Similar to i2c_smbus_read_word_data(), but - selects page first. - - int pmbus_write_word_data(struct i2c_client *client, u8 page, u8 reg, - u16 word); - - Write word data to <page>, <reg>. Similar to i2c_smbus_write_word_data(), but - selects page first. - - int pmbus_read_byte_data(struct i2c_client *client, int page, u8 reg); - - Read byte data from <page>, <reg>. Similar to i2c_smbus_read_byte_data(), but - selects page first. <page> may be -1, which means "current page". - - int pmbus_write_byte(struct i2c_client *client, int page, u8 value); - - Write byte data to <page>, <reg>. Similar to i2c_smbus_write_byte(), but - selects page first. <page> may be -1, which means "current page". - - void pmbus_clear_faults(struct i2c_client *client); - - Execute PMBus "Clear Fault" command on all chip pages. - This function calls the device specific write_byte function if defined. - Therefore, it must _not_ be called from that function. - - bool pmbus_check_byte_register(struct i2c_client *client, int page, int reg); - - Check if byte register exists. Return true if the register exists, false - otherwise. - This function calls the device specific write_byte function if defined to - obtain the chip status. Therefore, it must _not_ be called from that function. - - bool pmbus_check_word_register(struct i2c_client *client, int page, int reg); - - Check if word register exists. Return true if the register exists, false - otherwise. - This function calls the device specific write_byte function if defined to - obtain the chip status. Therefore, it must _not_ be called from that function. - - int pmbus_do_probe(struct i2c_client *client, const struct i2c_device_id *id, - struct pmbus_driver_info *info); - - Execute probe function. Similar to standard probe function for other drivers, - with the pointer to struct pmbus_driver_info as additional argument. Calls - identify function if supported. Must only be called from device probe - function. - - void pmbus_do_remove(struct i2c_client *client); - - Execute driver remove function. Similar to standard driver remove function. - - const struct pmbus_driver_info - *pmbus_get_driver_info(struct i2c_client *client); - - Return pointer to struct pmbus_driver_info as passed to pmbus_do_probe(). - - -PMBus driver platform data -========================== - -PMBus platform data is defined in include/linux/pmbus.h. Platform data -currently only provides a flag field with a single bit used. - -#define PMBUS_SKIP_STATUS_CHECK (1 << 0) - -struct pmbus_platform_data { - u32 flags; /* Device specific flags */ -}; - - -Flags ------ - -PMBUS_SKIP_STATUS_CHECK - -During register detection, skip checking the status register for -communication or command errors. - -Some PMBus chips respond with valid data when trying to read an unsupported -register. For such chips, checking the status register is mandatory when -trying to determine if a chip register exists or not. -Other PMBus chips don't support the STATUS_CML register, or report -communication errors for no explicable reason. For such chips, checking the -status register must be disabled. - -Some i2c controllers do not support single-byte commands (write commands with -no data, i2c_smbus_write_byte()). With such controllers, clearing the status -register is impossible, and the PMBUS_SKIP_STATUS_CHECK flag must be set. |