Linux i2c Subsystem

This is the home of the Linux i2c subsystem.

Theory of operation

• Driver Architecture
• I2C protocol summary
• SMBus protocol summary
• 10-bit addresses information
• /dev interface documentation
• I2C adapter functionalities
• I2C bus multiplexing
• complex I2C topologies

Developer's documentation

• Linux 2.6 I2C development FAQ
• Conventions for use of fault codes in the I2C/SMBus stack
• How to instantiate I2C devices
• Writing kernel drivers for I2C or SMBus devices
• i2c-stub, a fake I2C/SMBus master driver for testing purpose

User-space tools

User-space tools for I2C/SMBus are being maintained in the i2c-tools git tree. Released versions can be downloaded from https://www.kernel.org/pub/software/utils/i2c-tools/.

Work in progress

• increase SMBus max block size from 32 to 255 as documented in the 3.x specification. Hardest problem is to not break userspace ABI.

To-do list

• The i2c-dev driver needs to be ported to the new i2c device driver binding model. See this discussion and this bug report.
• i2c_adapter.retries and i2c_adapter.timeout need to be clarified. Their original intent was not necessarily good nor clear, but they could still be useful, if fault codes returned by adapter drivers are also clarified.
• Exclusive access to bus segments or devices. The former can partly be done in-kernel since version 3.6 (i2c_lock_adapter / __i2c_transfer / i2c_unlock_adapter) or the SMBus equivalent. Also the user-space case mentioned here is not supported yet.
• The kernel should be able to prevent probing of specific I2C bus segments from user-space. Either by exposing the class flags and hoping user-space will pay attention and be fair, or by defining one more class flag for user-space access and enforcing it.

Old pages

Subsystem History - up to Linux 3.6