1 .. SPDX-License-Identifier: GPL-2.0
2
3 ================================
4 Linux I2C slave testunit backend
5 ================================
6
7 by Wolfram Sang <wsa@sang-engineering.com> in 2020
8
9 This backend can be used to trigger test cases for I2C bus masters which
10 require a remote device with certain capabilities (and which are usually not so
11 easy to obtain). Examples include multi-master testing, and SMBus Host Notify
12 testing. For some tests, the I2C slave controller must be able to switch
13 between master and slave mode because it needs to send data, too.
14
15 Note that this is a device for testing and debugging. It should not be enabled
16 in a production build. And while there is some versioning and we try hard to
17 keep backward compatibility, there is no stable ABI guaranteed!
18
19 Instantiating the device is regular. Example for bus 0, address 0x30::
20
21 # echo "slave-testunit 0x1030" > /sys/bus/i2c/devices/i2c-0/new_device
22
23 Or using firmware nodes. Here is a devicetree example (note this is only a
24 debug device, so there are no official DT bindings)::
25
26 &i2c0 {
27 ...
28
29 testunit@30 {
30 compatible = "slave-testunit";
31 reg = <(0x30 | I2C_OWN_SLAVE_ADDRESS)>;
32 };
33 };
34
35 After that, you will have the device listening. Reading will return a single
36 byte. Its value is 0 if the testunit is idle, otherwise the command number of
37 the currently running command.
38
39 When writing, the device consists of 4 8-bit registers and, except for some
40 "partial" commands, all registers must be written to start a testcase, i.e. you
41 usually write 4 bytes to the device. The registers are:
42
43 .. csv-table::
44 :header: "Offset", "Name", "Description"
45
46 0x00, CMD, which test to trigger
47 0x01, DATAL, configuration byte 1 for the test
48 0x02, DATAH, configuration byte 2 for the test
49 0x03, DELAY, delay in n * 10ms until test is started
50
51 Using 'i2cset' from the i2c-tools package, the generic command looks like::
52
53 # i2cset -y <bus_num> <testunit_address> <CMD> <DATAL> <DATAH> <DELAY> i
54
55 DELAY is a generic parameter which will delay the execution of the test in CMD.
56 While a command is running (including the delay), new commands will not be
57 acknowledged. You need to wait until the old one is completed.
58
59 The commands are described in the following section. An invalid command will
60 result in the transfer not being acknowledged.
61
62 Commands
63 --------
64
65 0x00 NOOP
66 ~~~~~~~~~
67
68 Reserved for future use.
69
70 0x01 READ_BYTES
71 ~~~~~~~~~~~~~~~
72
73 .. list-table::
74 :header-rows: 1
75
76 * - CMD
77 - DATAL
78 - DATAH
79 - DELAY
80
81 * - 0x01
82 - address to read data from (lower 7 bits, highest bit currently unused)
83 - number of bytes to read
84 - n * 10ms
85
86 Also needs master mode. This is useful to test if your bus master driver is
87 handling multi-master correctly. You can trigger the testunit to read bytes
88 from another device on the bus. If the bus master under test also wants to
89 access the bus at the same time, the bus will be busy. Example to read 128
90 bytes from device 0x50 after 50ms of delay::
91
92 # i2cset -y 0 0x30 1 0x50 0x80 5 i
93
94 0x02 SMBUS_HOST_NOTIFY
95 ~~~~~~~~~~~~~~~~~~~~~~
96
97 .. list-table::
98 :header-rows: 1
99
100 * - CMD
101 - DATAL
102 - DATAH
103 - DELAY
104
105 * - 0x02
106 - low byte of the status word to send
107 - high byte of the status word to send
108 - n * 10ms
109
110 Also needs master mode. This test will send an SMBUS_HOST_NOTIFY message to the
111 host. Note that the status word is currently ignored in the Linux Kernel.
112 Example to send a notification with status word 0x6442 after 10ms::
113
114 # i2cset -y 0 0x30 2 0x42 0x64 1 i
115
116 If the host controller supports HostNotify, this message with debug level
117 should appear (Linux 6.11 and later)::
118
119 Detected HostNotify from address 0x30
120
121 0x03 SMBUS_BLOCK_PROC_CALL
122 ~~~~~~~~~~~~~~~~~~~~~~~~~~
123
124 .. list-table::
125 :header-rows: 1
126
127 * - CMD
128 - DATAL
129 - DATAH
130 - DELAY
131
132 * - 0x03
133 - 0x01 (i.e. one further byte will be written)
134 - number of bytes to be sent back
135 - leave out, partial command!
136
137 Partial command. This test will respond to a block process call as defined by
138 the SMBus specification. The one data byte written specifies how many bytes
139 will be sent back in the following read transfer. Note that in this read
140 transfer, the testunit will prefix the length of the bytes to follow. So, if
141 your host bus driver emulates SMBus calls like the majority does, it needs to
142 support the I2C_M_RECV_LEN flag of an i2c_msg. This is a good testcase for it.
143 The returned data consists of the length first, and then of an array of bytes
144 from length-1 to 0. Here is an example which emulates
145 i2c_smbus_block_process_call() using i2ctransfer (you need i2c-tools v4.2 or
146 later)::
147
148 # i2ctransfer -y 0 w3@0x30 3 1 0x10 r?
149 0x10 0x0f 0x0e 0x0d 0x0c 0x0b 0x0a 0x09 0x08 0x07 0x06 0x05 0x04 0x03 0x02 0x01 0x00
150
151 0x04 GET_VERSION_WITH_REP_START
152 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
153
154 .. list-table::
155 :header-rows: 1
156
157 * - CMD
158 - DATAL
159 - DATAH
160 - DELAY
161
162 * - 0x04
163 - currently unused
164 - currently unused
165 - leave out, partial command!
166
167 Partial command. After sending this command, the testunit will reply to a read
168 message with a NUL terminated version string based on UTS_RELEASE. The first
169 character is always a 'v' and the length of the version string is at maximum
170 128 bytes. However, it will only respond if the read message is connected to
171 the write message via repeated start. If your controller driver handles
172 repeated start correctly, this will work::
173
174 # i2ctransfer -y 0 w3@0x30 4 0 0 r128
175 0x76 0x36 0x2e 0x31 0x31 0x2e 0x30 0x2d 0x72 0x63 0x31 0x2d 0x30 0x30 0x30 0x30 ...
176
177 If you have i2c-tools 4.4 or later, you can print out the data right away::
178
179 # i2ctransfer -y -b 0 w3@0x30 4 0 0 r128
180 v6.11.0-rc1-00009-gd37a1b4d3fd0
181
182 STOP/START combinations between the two messages will *not* work because they
183 are not equivalent to a REPEATED START. As an example, this returns just the
184 default response::
185
186 # i2cset -y 0 0x30 4 0 0 i; i2cget -y 0 0x30
187 0x00
188
189 0x05 SMBUS_ALERT_REQUEST
190 ~~~~~~~~~~~~~~~~~~~~~~~~
191
192 .. list-table::
193 :header-rows: 1
194
195 * - CMD
196 - DATAL
197 - DATAH
198 - DELAY
199
200 * - 0x05
201 - response value (7 MSBs interpreted as I2C address)
202 - currently unused
203 - n * 10ms
204
205 This test raises an interrupt via the SMBAlert pin which the host controller
206 must handle. The pin must be connected to the testunit as a GPIO. GPIO access
207 is not allowed to sleep. Currently, this can only be described using firmware
208 nodes. So, for devicetree, you would add something like this to the testunit
209 node::
210
211 gpios = <&gpio1 24 GPIO_ACTIVE_LOW>;
212
213 The following command will trigger the alert with a response of 0xc9 after 1
214 second of delay::
215
216 # i2cset -y 0 0x30 5 0xc9 0x00 100 i
217
218 If the host controller supports SMBusAlert, this message with debug level
219 should appear::
220
221 smbus_alert 0-000c: SMBALERT# from dev 0x64, flag 1
222
223 This message may appear more than once because the testunit is software not
224 hardware and, thus, may not be able to react to the response of the host fast
225 enough. The interrupt count should increase only by one, though::
226
227 # cat /proc/interrupts | grep smbus_alert
228 93: 1 gpio-rcar 26 Edge smbus_alert
229
230 If the host does not respond to the alert within 1 second, the test will be
231 aborted and the testunit will report an error.
232
233 For this test, the testunit will shortly drop its assigned address and listen
234 on the SMBus Alert Response Address (0x0c). It will reassign its original
235 address afterwards.
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