1Mpp buffer design (2016.10.12) 2================================================================================ 3 4Mpp buffer is the warpper of the buffer used by hardware. Hardware usually can 5not use the buffer malloc by cpu. Then we design MppBuffer for different memory 6allocator on different platform. Currently it is designed for ion buffer on 7Android and drm buffer on Linux. Later may support vb2_buffer in v4l2 devices. 8 9In order to manage buffer usage in different user mpp buffer module introduces 10MppBufferGroup as bufffer manager. All MppBuffer will connect to its manager. 11MppBufferGroup provides allocator service and buffer reuse ability. 12 13Different MppBufferGroup has different allocator. And besides normal malloc/free 14function the allocator can also accept buffer from external file descriptor. 15 16MppBufferGroup has two lists, unused buffer list and used buffer list. When 17buffer is free buffer will not be released immediately. Buffer will be moved to 18unused list for later reuse. There is a good reason for doing so. When video 19resolution comes to 4K the buffer size will be above 12M. It will take a long 20time to allocate buffer and generate map table for it. So reusing the buffer 21will save the allocate/free time. 22 23Here is the diagram of Mpp buffer status transaction. 24 25 +----------+ +---------+ 26 | create | | commit | 27 +-----+----+ +----+----+ 28 | | 29 | | 30 | +----v----+ 31 +----------+ unused <-----------+ 32 | +---------+ | 33 | | | | 34 | | | | 35 +-----v----+ | | +-----+----+ 36 | malloc | | | | free | 37 +----------+ | | +----------+ 38 | inc_ref | +---------+ | dec_ref | 39 +-----+----+ +-----^----+ 40 | | 41 | | 42 | +---------+ | 43 +----------> used +-----------+ 44 +---------+ 45 | | 46 | | 47 | | 48 | | 49 | | 50 +----^----+ 51 | 52 | 53 +----+----+ 54 | import | 55 +---------+ 56 57 58