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1=================2SoundWire Locking3=================4 5This document explains locking mechanism of the SoundWire Bus. Bus uses6following locks in order to avoid race conditions in Bus operations on7shared resources.8 9 - Bus lock10 11 - Message lock12 13Bus lock14========15 16SoundWire Bus lock is a mutex and is part of Bus data structure17(sdw_bus) which is used for every Bus instance. This lock is used to18serialize each of the following operations(s) within SoundWire Bus instance.19 20 - Addition and removal of Slave(s), changing Slave status.21 22 - Prepare, Enable, Disable and De-prepare stream operations.23 24 - Access of Stream data structure.25 26Message lock27============28 29SoundWire message transfer lock. This mutex is part of30Bus data structure (sdw_bus). This lock is used to serialize the message31transfers (read/write) within a SoundWire Bus instance.32 33Below examples show how locks are acquired.34 35Example 136---------37 38Message transfer.39 40 1. For every message transfer41 42 a. Acquire Message lock.43 44 b. Transfer message (Read/Write) to Slave1 or broadcast message on45 Bus in case of bank switch.46 47 c. Release Message lock48 49 ::50 51 +----------+ +---------+52 | | | |53 | Bus | | Master |54 | | | Driver |55 | | | |56 +----+-----+ +----+----+57 | |58 | bus->ops->xfer_msg() |59 <-------------------------------+ a. Acquire Message lock60 | | b. Transfer message61 | |62 +-------------------------------> c. Release Message lock63 | return success/error | d. Return success/error64 | |65 + +66 67Example 268---------69 70Prepare operation.71 72 1. Acquire lock for Bus instance associated with Master 1.73 74 2. For every message transfer in Prepare operation75 76 a. Acquire Message lock.77 78 b. Transfer message (Read/Write) to Slave1 or broadcast message on79 Bus in case of bank switch.80 81 c. Release Message lock.82 83 3. Release lock for Bus instance associated with Master 1 ::84 85 +----------+ +---------+86 | | | |87 | Bus | | Master |88 | | | Driver |89 | | | |90 +----+-----+ +----+----+91 | |92 | sdw_prepare_stream() |93 <-------------------------------+ 1. Acquire bus lock94 | | 2. Perform stream prepare95 | |96 | |97 | bus->ops->xfer_msg() |98 <-------------------------------+ a. Acquire Message lock99 | | b. Transfer message100 | |101 +-------------------------------> c. Release Message lock102 | return success/error | d. Return success/error103 | |104 | |105 | return success/error | 3. Release bus lock106 +-------------------------------> 4. Return success/error107 | |108 + +109