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+======================
+SMBus Protocol Summary
+======================
+
+The following is a summary of the SMBus protocol. It applies to
+all revisions of the protocol (1.0, 1.1, and 2.0).
+Certain protocol features which are not supported by
+this package are briefly described at the end of this document.
+
+Some adapters understand only the SMBus (System Management Bus) protocol,
+which is a subset from the I2C protocol. Fortunately, many devices use
+only the same subset, which makes it possible to put them on an SMBus.
+
+If you write a driver for some I2C device, please try to use the SMBus
+commands if at all possible (if the device uses only that subset of the
+I2C protocol). This makes it possible to use the device driver on both
+SMBus adapters and I2C adapters (the SMBus command set is automatically
+translated to I2C on I2C adapters, but plain I2C commands can not be
+handled at all on most pure SMBus adapters).
+
+Below is a list of SMBus protocol operations, and the functions executing
+them.  Note that the names used in the SMBus protocol specifications usually
+don't match these function names.  For some of the operations which pass a
+single data byte, the functions using SMBus protocol operation names execute
+a different protocol operation entirely.
+
+Each transaction type corresponds to a functionality flag. Before calling a
+transaction function, a device driver should always check (just once) for
+the corresponding functionality flag to ensure that the underlying I2C
+adapter supports the transaction in question. See
+<file:Documentation/i2c/functionality.rst> for the details.
+
+
+Key to symbols
+==============
+
+=============== =============================================================
+S     (1 bit) : Start bit
+P     (1 bit) : Stop bit
+Rd/Wr (1 bit) : Read/Write bit. Rd equals 1, Wr equals 0.
+A, NA (1 bit) : Accept and reverse accept bit.
+Addr  (7 bits): I2C 7 bit address. Note that this can be expanded as usual to
+                get a 10 bit I2C address.
+Comm  (8 bits): Command byte, a data byte which often selects a register on
+                the device.
+Data  (8 bits): A plain data byte. Sometimes, I write DataLow, DataHigh
+                for 16 bit data.
+Count (8 bits): A data byte containing the length of a block operation.
+
+[..]:           Data sent by I2C device, as opposed to data sent by the host
+                adapter.
+=============== =============================================================
+
+
+SMBus Quick Command
+===================
+
+This sends a single bit to the device, at the place of the Rd/Wr bit::
+
+  A Addr Rd/Wr [A] P
+
+Functionality flag: I2C_FUNC_SMBUS_QUICK
+
+
+SMBus Receive Byte:  i2c_smbus_read_byte()
+==========================================
+
+This reads a single byte from a device, without specifying a device
+register. Some devices are so simple that this interface is enough; for
+others, it is a shorthand if you want to read the same register as in
+the previous SMBus command::
+
+  S Addr Rd [A] [Data] NA P
+
+Functionality flag: I2C_FUNC_SMBUS_READ_BYTE
+
+
+SMBus Send Byte:  i2c_smbus_write_byte()
+========================================
+
+This operation is the reverse of Receive Byte: it sends a single byte
+to a device.  See Receive Byte for more information.
+
+::
+
+  S Addr Wr [A] Data [A] P
+
+Functionality flag: I2C_FUNC_SMBUS_WRITE_BYTE
+
+
+SMBus Read Byte:  i2c_smbus_read_byte_data()
+============================================
+
+This reads a single byte from a device, from a designated register.
+The register is specified through the Comm byte::
+
+  S Addr Wr [A] Comm [A] S Addr Rd [A] [Data] NA P
+
+Functionality flag: I2C_FUNC_SMBUS_READ_BYTE_DATA
+
+
+SMBus Read Word:  i2c_smbus_read_word_data()
+============================================
+
+This operation is very like Read Byte; again, data is read from a
+device, from a designated register that is specified through the Comm
+byte. But this time, the data is a complete word (16 bits)::
+
+  S Addr Wr [A] Comm [A] S Addr Rd [A] [DataLow] A [DataHigh] NA P
+
+Functionality flag: I2C_FUNC_SMBUS_READ_WORD_DATA
+
+Note the convenience function i2c_smbus_read_word_swapped is
+available for reads where the two data bytes are the other way
+around (not SMBus compliant, but very popular.)
+
+
+SMBus Write Byte:  i2c_smbus_write_byte_data()
+==============================================
+
+This writes a single byte to a device, to a designated register. The
+register is specified through the Comm byte. This is the opposite of
+the Read Byte operation.
+
+::
+
+  S Addr Wr [A] Comm [A] Data [A] P
+
+Functionality flag: I2C_FUNC_SMBUS_WRITE_BYTE_DATA
+
+
+SMBus Write Word:  i2c_smbus_write_word_data()
+==============================================
+
+This is the opposite of the Read Word operation. 16 bits
+of data is written to a device, to the designated register that is
+specified through the Comm byte.::
+
+  S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A] P
+
+Functionality flag: I2C_FUNC_SMBUS_WRITE_WORD_DATA
+
+Note the convenience function i2c_smbus_write_word_swapped is
+available for writes where the two data bytes are the other way
+around (not SMBus compliant, but very popular.)
+
+
+SMBus Process Call:
+===================
+
+This command selects a device register (through the Comm byte), sends
+16 bits of data to it, and reads 16 bits of data in return::
+
+  S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A]
+                               S Addr Rd [A] [DataLow] A [DataHigh] NA P
+
+Functionality flag: I2C_FUNC_SMBUS_PROC_CALL
+
+
+SMBus Block Read:  i2c_smbus_read_block_data()
+==============================================
+
+This command reads a block of up to 32 bytes from a device, from a
+designated register that is specified through the Comm byte. The amount
+of data is specified by the device in the Count byte.
+
+::
+
+  S Addr Wr [A] Comm [A]
+             S Addr Rd [A] [Count] A [Data] A [Data] A ... A [Data] NA P
+
+Functionality flag: I2C_FUNC_SMBUS_READ_BLOCK_DATA
+
+
+SMBus Block Write:  i2c_smbus_write_block_data()
+================================================
+
+The opposite of the Block Read command, this writes up to 32 bytes to
+a device, to a designated register that is specified through the
+Comm byte. The amount of data is specified in the Count byte.
+
+::
+
+  S Addr Wr [A] Comm [A] Count [A] Data [A] Data [A] ... [A] Data [A] P
+
+Functionality flag: I2C_FUNC_SMBUS_WRITE_BLOCK_DATA
+
+
+SMBus Block Write - Block Read Process Call
+===========================================
+
+SMBus Block Write - Block Read Process Call was introduced in
+Revision 2.0 of the specification.
+
+This command selects a device register (through the Comm byte), sends
+1 to 31 bytes of data to it, and reads 1 to 31 bytes of data in return::
+
+  S Addr Wr [A] Comm [A] Count [A] Data [A] ...
+                               S Addr Rd [A] [Count] A [Data] ... A P
+
+Functionality flag: I2C_FUNC_SMBUS_BLOCK_PROC_CALL
+
+
+SMBus Host Notify
+=================
+
+This command is sent from a SMBus device acting as a master to the
+SMBus host acting as a slave.
+It is the same form as Write Word, with the command code replaced by the
+alerting device's address.
+
+::
+
+  [S] [HostAddr] [Wr] A [DevAddr] A [DataLow] A [DataHigh] A [P]
+
+This is implemented in the following way in the Linux kernel:
+
+* I2C bus drivers which support SMBus Host Notify should report
+  I2C_FUNC_SMBUS_HOST_NOTIFY.
+* I2C bus drivers trigger SMBus Host Notify by a call to
+  i2c_handle_smbus_host_notify().
+* I2C drivers for devices which can trigger SMBus Host Notify will have
+  client->irq assigned to a Host Notify IRQ if noone else specified an other.
+
+There is currently no way to retrieve the data parameter from the client.
+
+
+Packet Error Checking (PEC)
+===========================
+
+Packet Error Checking was introduced in Revision 1.1 of the specification.
+
+PEC adds a CRC-8 error-checking byte to transfers using it, immediately
+before the terminating STOP.
+
+
+Address Resolution Protocol (ARP)
+=================================
+
+The Address Resolution Protocol was introduced in Revision 2.0 of
+the specification. It is a higher-layer protocol which uses the
+messages above.
+
+ARP adds device enumeration and dynamic address assignment to
+the protocol. All ARP communications use slave address 0x61 and
+require PEC checksums.
+
+
+SMBus Alert
+===========
+
+SMBus Alert was introduced in Revision 1.0 of the specification.
+
+The SMBus alert protocol allows several SMBus slave devices to share a
+single interrupt pin on the SMBus master, while still allowing the master
+to know which slave triggered the interrupt.
+
+This is implemented the following way in the Linux kernel:
+
+* I2C bus drivers which support SMBus alert should call
+  i2c_setup_smbus_alert() to setup SMBus alert support.
+* I2C drivers for devices which can trigger SMBus alerts should implement
+  the optional alert() callback.
+
+
+I2C Block Transactions
+======================
+
+The following I2C block transactions are supported by the
+SMBus layer and are described here for completeness.
+They are *NOT* defined by the SMBus specification.
+
+I2C block transactions do not limit the number of bytes transferred
+but the SMBus layer places a limit of 32 bytes.
+
+
+I2C Block Read:  i2c_smbus_read_i2c_block_data()
+================================================
+
+This command reads a block of bytes from a device, from a
+designated register that is specified through the Comm byte::
+
+  S Addr Wr [A] Comm [A]
+             S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P
+
+Functionality flag: I2C_FUNC_SMBUS_READ_I2C_BLOCK
+
+
+I2C Block Write:  i2c_smbus_write_i2c_block_data()
+==================================================
+
+The opposite of the Block Read command, this writes bytes to
+a device, to a designated register that is specified through the
+Comm byte. Note that command lengths of 0, 2, or more bytes are
+supported as they are indistinguishable from data.
+
+::
+
+  S Addr Wr [A] Comm [A] Data [A] Data [A] ... [A] Data [A] P
+
+Functionality flag: I2C_FUNC_SMBUS_WRITE_I2C_BLOCK