1================= 2SoundWire Locking 3================= 4 5This document explains locking mechanism of the SoundWire Bus. Bus uses 6following locks in order to avoid race conditions in Bus operations on 7shared resources. 8 9 - Bus lock 10 11 - Message lock 12 13Bus lock 14======== 15 16SoundWire 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 18serialize 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 lock 27============ 28 29SoundWire message transfer lock. This mutex is part of 30Bus data structure (sdw_bus). This lock is used to serialize the message 31transfers (read/write) within a SoundWire Bus instance. 32 33Below examples show how locks are acquired. 34 35Example 1 36--------- 37 38Message transfer. 39 40 1. For every message transfer 41 42 a. Acquire Message lock. 43 44 b. Transfer message (Read/Write) to Slave1 or broadcast message on 45 Bus in case of bank switch. 46 47 c. Release Message lock 48 49 :: 50 51 +----------+ +---------+ 52 | | | | 53 | Bus | | Master | 54 | | | Driver | 55 | | | | 56 +----+-----+ +----+----+ 57 | | 58 | bus->ops->xfer_msg() | 59 <-------------------------------+ a. Acquire Message lock 60 | | b. Transfer message 61 | | 62 +-------------------------------> c. Release Message lock 63 | return success/error | d. Return success/error 64 | | 65 + + 66 67Example 2 68--------- 69 70Prepare operation. 71 72 1. Acquire lock for Bus instance associated with Master 1. 73 74 2. For every message transfer in Prepare operation 75 76 a. Acquire Message lock. 77 78 b. Transfer message (Read/Write) to Slave1 or broadcast message on 79 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 lock 94 | | 2. Perform stream prepare 95 | | 96 | | 97 | bus->ops->xfer_msg() | 98 <-------------------------------+ a. Acquire Message lock 99 | | b. Transfer message 100 | | 101 +-------------------------------> c. Release Message lock 102 | return success/error | d. Return success/error 103 | | 104 | | 105 | return success/error | 3. Release bus lock 106 +-------------------------------> 4. Return success/error 107 | | 108 + + 109