1 =================
2 SoundWire Locking
3 =================
4
5 This document explains locking mechanism of th
6 following locks in order to avoid race conditi
7 shared resources.
8
9 - Bus lock
10
11 - Message lock
12
13 Bus lock
14 ========
15
16 SoundWire Bus lock is a mutex and is part of B
17 (sdw_bus) which is used for every Bus instance
18 serialize each of the following operations(s)
19
20 - Addition and removal of Slave(s), changing
21
22 - Prepare, Enable, Disable and De-prepare st
23
24 - Access of Stream data structure.
25
26 Message lock
27 ============
28
29 SoundWire message transfer lock. This mutex is
30 Bus data structure (sdw_bus). This lock is use
31 transfers (read/write) within a SoundWire Bus
32
33 Below examples show how locks are acquired.
34
35 Example 1
36 ---------
37
38 Message transfer.
39
40 1. For every message transfer
41
42 a. Acquire Message lock.
43
44 b. Transfer message (Read/Write) to Slave
45 Bus in case of bank switch.
46
47 c. Release Message lock
48
49 ::
50
51 +----------+ +-----
52 | | |
53 | Bus | | Mast
54 | | | Driv
55 | | |
56 +----+-----+ +----+
57 | |
58 | bus->ops->xfer_msg() |
59 <-------------------------------+
60 | |
61 | |
62 +------------------------------->
63 | return success/error |
64 | |
65 + +
66
67 Example 2
68 ---------
69
70 Prepare operation.
71
72 1. Acquire lock for Bus instance associated
73
74 2. For every message transfer in Prepare ope
75
76 a. Acquire Message lock.
77
78 b. Transfer message (Read/Write) to Slave
79 Bus in case of bank switch.
80
81 c. Release Message lock.
82
83 3. Release lock for Bus instance associated
84
85 +----------+ +-----
86 | | |
87 | Bus | | Mast
88 | | | Driv
89 | | |
90 +----+-----+ +----+
91 | |
92 | sdw_prepare_stream() |
93 <-------------------------------+
94 | |
95 | |
96 | |
97 | bus->ops->xfer_msg() |
98 <-------------------------------+
99 | |
100 | |
101 +------------------------------->
102 | return success/error |
103 | |
104 | |
105 | return success/error |
106 +------------------------------->
107 | |
108 + +
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