1 ======== 1 ========
2 i2c-stub 2 i2c-stub
3 ======== 3 ========
4 4
5 Description 5 Description
6 =========== 6 ===========
7 7
8 This module is a very simple fake I2C/SMBus dr 8 This module is a very simple fake I2C/SMBus driver. It implements six
9 types of SMBus commands: write quick, (r/w) by 9 types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, (r/w)
10 word data, (r/w) I2C block data, and (r/w) SMB 10 word data, (r/w) I2C block data, and (r/w) SMBus block data.
11 11
12 You need to provide chip addresses as a module 12 You need to provide chip addresses as a module parameter when loading this
13 driver, which will then only react to SMBus co 13 driver, which will then only react to SMBus commands to these addresses.
14 14
15 No hardware is needed nor associated with this 15 No hardware is needed nor associated with this module. It will accept write
16 quick commands to the specified addresses; it 16 quick commands to the specified addresses; it will respond to the other
17 commands (also to the specified addresses) by 17 commands (also to the specified addresses) by reading from or writing to
18 arrays in memory. It will also spam the kerne 18 arrays in memory. It will also spam the kernel logs for every command it
19 handles. 19 handles.
20 20
21 A pointer register with auto-increment is impl 21 A pointer register with auto-increment is implemented for all byte
22 operations. This allows for continuous byte r 22 operations. This allows for continuous byte reads like those supported by
23 EEPROMs, among others. 23 EEPROMs, among others.
24 24
25 SMBus block command support is disabled by def 25 SMBus block command support is disabled by default, and must be enabled
26 explicitly by setting the respective bits (0x0 26 explicitly by setting the respective bits (0x03000000) in the functionality
27 module parameter. 27 module parameter.
28 28
29 SMBus block commands must be written to config 29 SMBus block commands must be written to configure an SMBus command for
30 SMBus block operations. Writes can be partial. 30 SMBus block operations. Writes can be partial. Block read commands always
31 return the number of bytes selected with the l 31 return the number of bytes selected with the largest write so far.
32 32
33 The typical use-case is like this: 33 The typical use-case is like this:
34 34
35 1. load this module 35 1. load this module
36 2. use i2cset (from the i2c-tools proj 36 2. use i2cset (from the i2c-tools project) to pre-load some data
37 3. load the target chip driver module 37 3. load the target chip driver module
38 4. observe its behavior in the kernel 38 4. observe its behavior in the kernel log
39 39
40 There's a script named i2c-stub-from-dump in t 40 There's a script named i2c-stub-from-dump in the i2c-tools package which
41 can load register values automatically from a 41 can load register values automatically from a chip dump.
42 42
43 Parameters 43 Parameters
44 ========== 44 ==========
45 45
46 int chip_addr[10]: 46 int chip_addr[10]:
47 The SMBus addresses to emulate chips a 47 The SMBus addresses to emulate chips at.
48 48
49 unsigned long functionality: 49 unsigned long functionality:
50 Functionality override, to disable som 50 Functionality override, to disable some commands. See I2C_FUNC_*
51 constants in <linux/i2c.h> for the sui 51 constants in <linux/i2c.h> for the suitable values. For example,
52 value 0x1f0000 would only enable the q 52 value 0x1f0000 would only enable the quick, byte and byte data
53 commands. 53 commands.
54 54
55 u8 bank_reg[10], u8 bank_mask[10], u8 bank_sta 55 u8 bank_reg[10], u8 bank_mask[10], u8 bank_start[10], u8 bank_end[10]:
56 Optional bank settings. They tell whic 56 Optional bank settings. They tell which bits in which register
57 select the active bank, as well as the 57 select the active bank, as well as the range of banked registers.
58 58
59 Caveats 59 Caveats
60 ======= 60 =======
61 61
62 If your target driver polls some byte or word 62 If your target driver polls some byte or word waiting for it to change, the
63 stub could lock it up. Use i2cset to unlock i 63 stub could lock it up. Use i2cset to unlock it.
64 64
65 If you spam it hard enough, printk can be loss 65 If you spam it hard enough, printk can be lossy. This module really wants
66 something like relayfs. 66 something like relayfs.
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