67 lines
2.3 KiB
ReStructuredText
67 lines
2.3 KiB
ReStructuredText
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========
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i2c-stub
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========
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Description
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===========
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This module is a very simple fake I2C/SMBus driver. It implements six
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types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, (r/w)
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word data, (r/w) I2C block data, and (r/w) SMBus block data.
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You need to provide chip addresses as a module parameter when loading this
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driver, which will then only react to SMBus commands to these addresses.
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No hardware is needed nor associated with this module. It will accept write
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quick commands to the specified addresses; it will respond to the other
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commands (also to the specified addresses) by reading from or writing to
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arrays in memory. It will also spam the kernel logs for every command it
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handles.
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A pointer register with auto-increment is implemented for all byte
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operations. This allows for continuous byte reads like those supported by
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EEPROMs, among others.
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SMBus block command support is disabled by default, and must be enabled
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explicitly by setting the respective bits (0x03000000) in the functionality
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module parameter.
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SMBus block commands must be written to configure an SMBus command for
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SMBus block operations. Writes can be partial. Block read commands always
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return the number of bytes selected with the largest write so far.
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The typical use-case is like this:
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1. load this module
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2. use i2cset (from the i2c-tools project) to pre-load some data
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3. load the target chip driver module
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4. observe its behavior in the kernel log
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There's a script named i2c-stub-from-dump in the i2c-tools package which
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can load register values automatically from a chip dump.
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Parameters
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==========
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int chip_addr[10]:
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The SMBus addresses to emulate chips at.
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unsigned long functionality:
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Functionality override, to disable some commands. See I2C_FUNC_*
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constants in <linux/i2c.h> for the suitable values. For example,
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value 0x1f0000 would only enable the quick, byte and byte data
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commands.
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u8 bank_reg[10], u8 bank_mask[10], u8 bank_start[10], u8 bank_end[10]:
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Optional bank settings. They tell which bits in which register
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select the active bank, as well as the range of banked registers.
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Caveats
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=======
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If your target driver polls some byte or word waiting for it to change, the
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stub could lock it up. Use i2cset to unlock it.
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If you spam it hard enough, printk can be lossy. This module really wants
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something like relayfs.
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