1 =====================
2 I2C/SMBUS Fault Codes
3 =====================
4
5 This is a summary of the most important conven
6 codes in the I2C/SMBus stack.
7
8
9 A "Fault" is not always an "Error"
10 ----------------------------------
11 Not all fault reports imply errors; "page faul
12 example. Software often retries idempotent op
13 faults. There may be fancier recovery schemes
14 some cases, such as re-initializing (and maybe
15 recovery, triggered by a fault report, there i
16
17 In a similar way, sometimes a "fault" code jus
18 result for an operation ... it doesn't indicat
19 at all, just that the outcome wasn't on the "g
20
21 In short, your I2C driver code may need to kno
22 to respond correctly. Other code may need to
23 the right fault code, so that it can (in turn)
24
25
26 I2C and SMBus fault codes
27 -------------------------
28 These are returned as negative numbers from mo
29 some positive number indicating a non-fault re
30 numbers associated with these symbols differ b
31 though most Linux systems use <asm-generic/err
32
33 Note that the descriptions here are not exhaus
34 codes that may be returned, and other cases wh
35 be returned. However, drivers should not retu
36 cases (unless the hardware doesn't provide uni
37
38 Also, codes returned by adapter probe methods
39 specific to their host bus (such as PCI, or th
40
41
42 EAFNOSUPPORT
43 Returned by I2C adapters not supportin
44 they are requested to use such an addr
45
46 EAGAIN
47 Returned by I2C adapters when they los
48 transmit mode: some other master was
49 data at the same time.
50
51 Also returned when trying to invoke an
52 atomic context, when some task is alre
53 to execute some other operation.
54
55 EBADMSG
56 Returned by SMBus logic when an invali
57 is received. This code is a CRC cover
58 transaction, and is sent before the te
59 fault is only reported on read transac
60 may have a way to report PEC mismatche
61 host. Note that even if PECs are in u
62 on these as the only way to detect inc
63
64 EBUSY
65 Returned by SMBus adapters when the bu
66 than allowed. This usually indicates
67 SMBus adapter) needs some fault recove
68 or that the reset was attempted but fa
69
70 EINVAL
71 This rather vague error means an inval
72 detected before any I/O operation was
73 specific fault code when you can.
74
75 EIO
76 This rather vague error means somethin
77 performing an I/O operation. Use a mo
78 code when you can.
79
80 ENODEV
81 Returned by driver probe() methods. T
82 specific than ENXIO, implying the prob
83 address, but with the device found the
84 may verify the device returns *correct
85 return this as appropriate. (The driv
86 about probe faults other than ENXIO an
87
88 ENOMEM
89 Returned by any component that can't a
90 it needs to do so.
91
92 ENXIO
93 Returned by I2C adapters to indicate t
94 of a transfer didn't get an ACK. Whil
95 an I2C device was temporarily not resp
96 means there's nothing listening at tha
97
98 Returned by driver probe() methods to
99 found no device to bind to. (ENODEV m
100
101 EOPNOTSUPP
102 Returned by an adapter when asked to p
103 that it doesn't, or can't, support.
104
105 For example, this would be returned wh
106 doesn't support SMBus block transfers
107 one. In that case, the driver making
108 have verified that functionality was s
109 made that block transfer request.
110
111 Similarly, if an I2C adapter can't exe
112 messages, it should return this when a
113 transaction it can't. (These limitati
114 the adapter's functionality mask, sinc
115 that if an adapter supports I2C it sup
116
117 EPROTO
118 Returned when slave does not conform t
119 or SMBus (or chip-specific) protocol s
120 case is when the length of an SMBus bl
121 (from the SMBus slave) is outside the
122
123 ESHUTDOWN
124 Returned when a transfer was requested
125 which is already suspended.
126
127 ETIMEDOUT
128 This is returned by drivers when an op
129 time, and was aborted before it comple
130
131 SMBus adapters may return it when an o
132 time than allowed by the SMBus specifi
133 when a slave stretches clocks too far.
134 timeouts, but it's normal for I2C adap
135 arbitrary limits (much longer than SMB
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