1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 The Virtual PCM Test Driver 3 The Virtual PCM Test Driver
4 =========================== 4 ===========================
5 5
6 The Virtual PCM Test Driver emulates a generic 6 The Virtual PCM Test Driver emulates a generic PCM device, and can be used for
7 testing/fuzzing of the userspace ALSA applicat 7 testing/fuzzing of the userspace ALSA applications, as well as for testing/fuzzing of
8 the PCM middle layer. Additionally, it can be 8 the PCM middle layer. Additionally, it can be used for simulating hard to reproduce
9 problems with PCM devices. 9 problems with PCM devices.
10 10
11 What can this driver do? 11 What can this driver do?
12 ~~~~~~~~~~~~~~~~~~~~~~~~ 12 ~~~~~~~~~~~~~~~~~~~~~~~~
13 13
14 At this moment the driver can do the following 14 At this moment the driver can do the following things:
15 * Simulate both capture and playback p 15 * Simulate both capture and playback processes
16 * Generate random or pattern-based cap 16 * Generate random or pattern-based capturing data
17 * Inject delays into the playback and 17 * Inject delays into the playback and capturing processes
18 * Inject errors during the PCM callbac 18 * Inject errors during the PCM callbacks
19 19
20 It supports up to 8 substreams and 4 channels. 20 It supports up to 8 substreams and 4 channels. Also it supports both interleaved and
21 non-interleaved access modes. 21 non-interleaved access modes.
22 22
23 Also, this driver can check the playback strea 23 Also, this driver can check the playback stream for containing the predefined pattern,
24 which is used in the corresponding selftest (a 24 which is used in the corresponding selftest (alsa/pcmtest-test.sh) to check the PCM middle
25 layer data transferring functionality. Additio 25 layer data transferring functionality. Additionally, this driver redefines the default
26 RESET ioctl, and the selftest covers this PCM 26 RESET ioctl, and the selftest covers this PCM API functionality as well.
27 27
28 Configuration 28 Configuration
29 ------------- 29 -------------
30 30
31 The driver has several parameters besides the 31 The driver has several parameters besides the common ALSA module parameters:
32 32
33 * fill_mode (bool) - Buffer fill mode 33 * fill_mode (bool) - Buffer fill mode (see below)
34 * inject_delay (int) 34 * inject_delay (int)
35 * inject_hwpars_err (bool) 35 * inject_hwpars_err (bool)
36 * inject_prepare_err (bool) 36 * inject_prepare_err (bool)
37 * inject_trigger_err (bool) 37 * inject_trigger_err (bool)
38 38
39 39
40 Capture Data Generation 40 Capture Data Generation
41 ----------------------- 41 -----------------------
42 42
43 The driver has two modes of data generation: t 43 The driver has two modes of data generation: the first (0 in the fill_mode parameter)
44 means random data generation, the second (1 in 44 means random data generation, the second (1 in the fill_mode) - pattern-based
45 data generation. Let's look at the second mode 45 data generation. Let's look at the second mode.
46 46
47 First of all, you may want to specify the patt 47 First of all, you may want to specify the pattern for data generation. You can do it
48 by writing the pattern to the debugfs file. Th 48 by writing the pattern to the debugfs file. There are pattern buffer debugfs entries
49 for each channel, as well as entries which con 49 for each channel, as well as entries which contain the pattern buffer length.
50 50
51 * /sys/kernel/debug/pcmtest/fill_patte 51 * /sys/kernel/debug/pcmtest/fill_pattern[0-3]
52 * /sys/kernel/debug/pcmtest/fill_patte 52 * /sys/kernel/debug/pcmtest/fill_pattern[0-3]_len
53 53
54 To set the pattern for the channel 0 you can e 54 To set the pattern for the channel 0 you can execute the following command:
55 55
56 .. code-block:: bash 56 .. code-block:: bash
57 57
58 echo -n mycoolpattern > /sys/kernel/de 58 echo -n mycoolpattern > /sys/kernel/debug/pcmtest/fill_pattern0
59 59
60 Then, after every capture action performed on 60 Then, after every capture action performed on the 'pcmtest' device the buffer for the
61 channel 0 will contain 'mycoolpatternmycoolpat 61 channel 0 will contain 'mycoolpatternmycoolpatternmycoolpatternmy...'.
62 62
63 The pattern itself can be up to 4096 bytes lon 63 The pattern itself can be up to 4096 bytes long.
64 64
65 Delay injection 65 Delay injection
66 --------------- 66 ---------------
67 67
68 The driver has 'inject_delay' parameter, which 68 The driver has 'inject_delay' parameter, which has very self-descriptive name and
69 can be used for time delay/speedup simulations 69 can be used for time delay/speedup simulations. The parameter has integer type, and
70 it means the delay added between module's inte 70 it means the delay added between module's internal timer ticks.
71 71
72 If the 'inject_delay' value is positive, the b 72 If the 'inject_delay' value is positive, the buffer will be filled slower, if it is
73 negative - faster. You can try it yourself by 73 negative - faster. You can try it yourself by starting a recording in any
74 audiorecording application (like Audacity) and 74 audiorecording application (like Audacity) and selecting the 'pcmtest' device as a
75 source. 75 source.
76 76
77 This parameter can be also used for generating 77 This parameter can be also used for generating a huge amount of sound data in a very
78 short period of time (with the negative 'injec 78 short period of time (with the negative 'inject_delay' value).
79 79
80 Errors injection 80 Errors injection
81 ---------------- 81 ----------------
82 82
83 This module can be used for injecting errors i 83 This module can be used for injecting errors into the PCM communication process. This
84 action can help you to figure out how the user 84 action can help you to figure out how the userspace ALSA program behaves under unusual
85 circumstances. 85 circumstances.
86 86
87 For example, you can make all 'hw_params' PCM 87 For example, you can make all 'hw_params' PCM callback calls return EBUSY error by
88 writing '1' to the 'inject_hwpars_err' module 88 writing '1' to the 'inject_hwpars_err' module parameter:
89 89
90 .. code-block:: bash 90 .. code-block:: bash
91 91
92 echo 1 > /sys/module/snd_pcmtest/param 92 echo 1 > /sys/module/snd_pcmtest/parameters/inject_hwpars_err
93 93
94 Errors can be injected into the following PCM 94 Errors can be injected into the following PCM callbacks:
95 95
96 * hw_params (EBUSY) 96 * hw_params (EBUSY)
97 * prepare (EINVAL) 97 * prepare (EINVAL)
98 * trigger (EINVAL) 98 * trigger (EINVAL)
99 99
100 Playback test 100 Playback test
101 ------------- 101 -------------
102 102
103 This driver can be also used for the playback 103 This driver can be also used for the playback functionality testing - every time you
104 write the playback data to the 'pcmtest' PCM d 104 write the playback data to the 'pcmtest' PCM device and close it, the driver checks the
105 buffer for containing the looped pattern (whic 105 buffer for containing the looped pattern (which is specified in the fill_pattern
106 debugfs file for each channel). If the playbac 106 debugfs file for each channel). If the playback buffer content represents the looped
107 pattern, 'pc_test' debugfs entry is set into ' 107 pattern, 'pc_test' debugfs entry is set into '1'. Otherwise, the driver sets it to '0'.
108 108
109 ioctl redefinition test 109 ioctl redefinition test
110 ----------------------- 110 -----------------------
111 111
112 The driver redefines the 'reset' ioctl, which 112 The driver redefines the 'reset' ioctl, which is default for all PCM devices. To test
113 this functionality, we can trigger the reset i 113 this functionality, we can trigger the reset ioctl and check the 'ioctl_test' debugfs
114 entry: 114 entry:
115 115
116 .. code-block:: bash 116 .. code-block:: bash
117 117
118 cat /sys/kernel/debug/pcmtest/ioctl_te 118 cat /sys/kernel/debug/pcmtest/ioctl_test
119 119
120 If the ioctl is triggered successfully, this f 120 If the ioctl is triggered successfully, this file will contain '1', and '0' otherwise.
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