1 files changed, 216 insertions, 0 deletions

diff --git a/Documentation/i2c/smbus-protocol b/Documentation/i2c/smbus-protocol
new file mode 100644
index 000000000000..09f5e5ca4927
--- /dev/null
+++ b/Documentation/i2c/smbus-protocol
@@ -0,0 +1,216 @@
+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 commands.
+
+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 Write Quick
+=================
+
+This sends a single bit to the device, at the place of the Rd/Wr bit.
+There is no equivalent Read Quick command.
+
+A Addr Rd/Wr [A] P
+
+
+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
+
+
+SMBus Write Byte
+================
+
+This is the reverse of Read Byte: it sends a single byte to a device.
+See Read Byte for more information.
+
+S Addr Wr [A] Data [A] P
+
+
+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
+
+
+SMBus Read Word Data
+====================
+
+This command is very like Read Byte Data; 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
+
+
+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 Data command.
+
+S Addr Wr [A] Comm [A] Data [A] P
+
+
+SMBus Write Word Data
+=====================
+
+This is the opposite operation of the Read Word Data command. 16 bits
+of data is read from a device, from a designated register that is 
+specified through the Comm byte. 
+
+S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A] P
+
+
+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
+
+
+SMBus Block Read
+================
+
+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
+
+
+SMBus Block Write
+=================
+
+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
+
+
+SMBus Block Process Call
+========================
+
+SMBus Block 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
+
+
+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]
+
+
+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 all transfers.
+
+
+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.
+
+
+I2C Block Transactions
+======================
+The following I2C block transactions are supported by the
+SMBus layer and are described here for completeness.
+I2C block transactions do not limit the number of bytes transferred
+but the SMBus layer places a limit of 32 bytes.
+
+
+I2C Block Read
+==============
+
+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
+
+
+I2C Block Read (2 Comm bytes)
+=============================
+
+This command reads a block of bytes from a device, from a 
+designated register that is specified through the two Comm bytes.
+
+S Addr Wr [A] Comm1 [A] Comm2 [A] 
+           S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P
+
+
+I2C Block Write
+===============
+
+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
+
+