1 ================= 1 =================
2 SoundWire Locking 2 SoundWire Locking
3 ================= 3 =================
4 4
5 This document explains locking mechanism of th 5 This document explains locking mechanism of the SoundWire Bus. Bus uses
6 following locks in order to avoid race conditi 6 following locks in order to avoid race conditions in Bus operations on
7 shared resources. 7 shared resources.
8 8
9 - Bus lock 9 - Bus lock
10 10
11 - Message lock 11 - Message lock
12 12
13 Bus lock 13 Bus lock
14 ======== 14 ========
15 15
16 SoundWire Bus lock is a mutex and is part of B 16 SoundWire Bus lock is a mutex and is part of Bus data structure
17 (sdw_bus) which is used for every Bus instance 17 (sdw_bus) which is used for every Bus instance. This lock is used to
18 serialize each of the following operations(s) 18 serialize each of the following operations(s) within SoundWire Bus instance.
19 19
20 - Addition and removal of Slave(s), changing 20 - Addition and removal of Slave(s), changing Slave status.
21 21
22 - Prepare, Enable, Disable and De-prepare st 22 - Prepare, Enable, Disable and De-prepare stream operations.
23 23
24 - Access of Stream data structure. 24 - Access of Stream data structure.
25 25
26 Message lock 26 Message lock
27 ============ 27 ============
28 28
29 SoundWire message transfer lock. This mutex is 29 SoundWire message transfer lock. This mutex is part of
30 Bus data structure (sdw_bus). This lock is use 30 Bus data structure (sdw_bus). This lock is used to serialize the message
31 transfers (read/write) within a SoundWire Bus 31 transfers (read/write) within a SoundWire Bus instance.
32 32
33 Below examples show how locks are acquired. 33 Below examples show how locks are acquired.
34 34
35 Example 1 35 Example 1
36 --------- 36 ---------
37 37
38 Message transfer. 38 Message transfer.
39 39
40 1. For every message transfer 40 1. For every message transfer
41 41
42 a. Acquire Message lock. 42 a. Acquire Message lock.
43 43
44 b. Transfer message (Read/Write) to Slave 44 b. Transfer message (Read/Write) to Slave1 or broadcast message on
45 Bus in case of bank switch. 45 Bus in case of bank switch.
46 46
47 c. Release Message lock !! 47 c. Release Message lock ::
48 <<
49 :: <<
50 48
51 +----------+ +----- 49 +----------+ +---------+
52 | | | 50 | | | |
53 | Bus | | Mast 51 | Bus | | Master |
54 | | | Driv 52 | | | Driver |
55 | | | 53 | | | |
56 +----+-----+ +----+ 54 +----+-----+ +----+----+
57 | | 55 | |
58 | bus->ops->xfer_msg() | 56 | bus->ops->xfer_msg() |
59 <-------------------------------+ 57 <-------------------------------+ a. Acquire Message lock
60 | | 58 | | b. Transfer message
61 | | 59 | |
62 +-------------------------------> 60 +-------------------------------> c. Release Message lock
63 | return success/error | 61 | return success/error | d. Return success/error
64 | | 62 | |
65 + + 63 + +
66 64
67 Example 2 65 Example 2
68 --------- 66 ---------
69 67
70 Prepare operation. 68 Prepare operation.
71 69
72 1. Acquire lock for Bus instance associated 70 1. Acquire lock for Bus instance associated with Master 1.
73 71
74 2. For every message transfer in Prepare ope 72 2. For every message transfer in Prepare operation
75 73
76 a. Acquire Message lock. 74 a. Acquire Message lock.
77 75
78 b. Transfer message (Read/Write) to Slave 76 b. Transfer message (Read/Write) to Slave1 or broadcast message on
79 Bus in case of bank switch. 77 Bus in case of bank switch.
80 78
81 c. Release Message lock. 79 c. Release Message lock.
82 80
83 3. Release lock for Bus instance associated 81 3. Release lock for Bus instance associated with Master 1 ::
84 82
85 +----------+ +----- 83 +----------+ +---------+
86 | | | 84 | | | |
87 | Bus | | Mast 85 | Bus | | Master |
88 | | | Driv 86 | | | Driver |
89 | | | 87 | | | |
90 +----+-----+ +----+ 88 +----+-----+ +----+----+
91 | | 89 | |
92 | sdw_prepare_stream() | 90 | sdw_prepare_stream() |
93 <-------------------------------+ 91 <-------------------------------+ 1. Acquire bus lock
94 | | 92 | | 2. Perform stream prepare
95 | | 93 | |
96 | | 94 | |
97 | bus->ops->xfer_msg() | 95 | bus->ops->xfer_msg() |
98 <-------------------------------+ 96 <-------------------------------+ a. Acquire Message lock
99 | | 97 | | b. Transfer message
100 | | 98 | |
101 +-------------------------------> 99 +-------------------------------> c. Release Message lock
102 | return success/error | 100 | return success/error | d. Return success/error
103 | | 101 | |
104 | | 102 | |
105 | return success/error | 103 | return success/error | 3. Release bus lock
106 +-------------------------------> 104 +-------------------------------> 4. Return success/error
107 | | 105 | |
108 + + 106 + +
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