5 This document explains locking mechanism of the SoundWire Bus. Bus uses
6 following locks in order to avoid race conditions in Bus operations on
16 SoundWire Bus lock is a mutex and is part of Bus data structure
17 (sdw_bus) which is used for every Bus instance. This lock is used to
18 serialize each of the following operations(s) within SoundWire Bus instance.
20 - Addition and removal of Slave(s), changing Slave status.
22 - Prepare, Enable, Disable and De-prepare stream operations.
24 - Access of Stream data structure.
29 SoundWire message transfer lock. This mutex is part of
30 Bus data structure (sdw_bus). This lock is used to serialize the message
31 transfers (read/write) within a SoundWire Bus instance.
33 Below examples show how locks are acquired.
40 1. For every message transfer
42 a. Acquire Message lock.
44 b. Transfer message (Read/Write) to Slave1 or broadcast message on
45 Bus in case of bank switch.
47 c. Release Message lock ::
49 +----------+ +---------+
54 +----+-----+ +----+----+
56 | bus->ops->xfer_msg() |
57 <-------------------------------+ a. Acquire Message lock
58 | | b. Transfer message
60 +-------------------------------> c. Release Message lock
61 | return success/error | d. Return success/error
70 1. Acquire lock for Bus instance associated with Master 1.
72 2. For every message transfer in Prepare operation
74 a. Acquire Message lock.
76 b. Transfer message (Read/Write) to Slave1 or broadcast message on
77 Bus in case of bank switch.
79 c. Release Message lock.
81 3. Release lock for Bus instance associated with Master 1 ::
83 +----------+ +---------+
88 +----+-----+ +----+----+
90 | sdw_prepare_stream() |
91 <-------------------------------+ 1. Acquire bus lock
92 | | 2. Perform stream prepare
95 | bus->ops->xfer_msg() |
96 <-------------------------------+ a. Acquire Message lock
97 | | b. Transfer message
99 +-------------------------------> c. Release Message lock
100 | return success/error | d. Return success/error
103 | return success/error | 3. Release bus lock
104 +-------------------------------> 4. Return success/error