developer | 02e6591 | 2023-08-17 16:33:10 +0800 | [diff] [blame] | 1 | +=============================================================================+ |
| 2 | | Copyright (c) 2010-2020 Rambus, Inc. and/or its subsidiaries. | |
| 3 | | | |
| 4 | | Subject : DMABuf API Implementation Notes | |
| 5 | | Product : SLAD API | |
| 6 | | Date : 18 November, 2020 | |
| 7 | | | |
| 8 | +=============================================================================+ |
| 9 | |
| 10 | SLAD API Implementation Notes : DMABuf API |
| 11 | ========================================== |
| 12 | |
| 13 | The SLAD API is a set of the API's one of which is the DMA Buffer |
| 14 | Allocation (DMABuf) API. The driver implementation specifics of these APIs |
| 15 | are described in short documents that serve as an addendum to the API |
| 16 | specifications. This document describes the DMABuf API. |
| 17 | |
| 18 | |
| 19 | DMABuf API |
| 20 | ---------- |
| 21 | |
| 22 | The implementation of this API is fully re-entrant. |
| 23 | |
| 24 | Supported properties: |
| 25 | Alignment must be 1, 2, 4, 8, 16, 32, 64 or 128. |
| 26 | Bank is used to select a memory pool suitable for certain data types. |
| 27 | fCached can be used to indicate whether a DMA resource is cached. |
| 28 | Implementations of the DMAResource API can ignore the fCached parameter |
| 29 | and force all buffers to be allocated or registered either |
| 30 | cached or non-cached. |
| 31 | |
| 32 | DMABuf_NULLHandle: |
| 33 | Implemented as a NULL handle that can be assigned to a variable |
| 34 | of type DMABuf_Handle_t |
| 35 | |
| 36 | DMABuf_Handle_IsSame: |
| 37 | Two pointers to memory locations where the handles are stored |
| 38 | should be provided to this function as parameters. |
| 39 | The function will do byte comparison for the size of the handle type. |
| 40 | |
| 41 | DMABuf_Alloc: |
| 42 | Maximum buffer size supported is 1 megabyte. |
| 43 | Implementation uses the DMAResource API |
| 44 | |
| 45 | DMABuf_Register: |
| 46 | Supported values for AllocatorRef: |
| 47 | 'N' to register a buffer that is not intended to be DMA-safe but for |
| 48 | which a DMABuf handle is desired nevertheless. |
| 49 | 'R' to register a (subrange of) a buffer previously allocated with |
| 50 | DMABuf_Alloc. This buffer is known to be DMA-safe. |
| 51 | 'k' to register a buffer allocated with Linux kmalloc. |
| 52 | 'C' to register a coherent DMA-mapped buffer. The application must |
| 53 | provide the bus address in Alternative_p. |
| 54 | |
| 55 | Alternative_p is only used with allocator ref 'C' and should be set to |
| 56 | "NULL" for other allocators. |
| 57 | |
| 58 | All implementations of the DMAResource API support the 'N' and 'R' |
| 59 | allocators. The 'k' and 'C' allocators are only supported by |
| 60 | the Linux kernel implementation. |
| 61 | |
| 62 | DMABuf_Release: |
| 63 | The implementation is protected against invalid handles and also detects |
| 64 | and warns when handles are used after release (does not work well when |
| 65 | all available handles are in use). |
| 66 | |
| 67 | Banks: |
| 68 | The implementation supports several banks. The banks are configurable, |
| 69 | an example default configuration is as follows |
| 70 | (bank values in DMABuf_Properties_t): |
| 71 | |
| 72 | - Bank 0 allocates buffers anywhere in physical RAM without restrictions. |
| 73 | |
| 74 | - Bank 1 allocates buffers suitable for SA records and Transform records. |
| 75 | All these are required to lie in a single 4GB segment on 64-bit systems. |
| 76 | |
| 77 | - Bank 2 allocates buffers suitable for flow records. All these are |
| 78 | required to lie in a single 4GB segment on 64-bit systems. |
| 79 | |
| 80 | The following properties of the static (fixed-size) DMA banks are implemented: |
| 81 | |
| 82 | - One static bank contains one DMA pool; |
| 83 | |
| 84 | - One DMA Pool contains a fixed compile-time configurable number of blocks; |
| 85 | |
| 86 | - All blocks in one DMA pool have the same fixed compile-time configurable |
| 87 | size; |
| 88 | |
| 89 | - The DMA pools for all the configured static banks are allocated |
| 90 | in DMAResource_Init() and freed in DMAResource_Uninit(); |
| 91 | |
| 92 | - DMA resources can be allocated in a static bank using |
| 93 | DMABuf_Alloc() and they must be freed using DMABuf_Release(); |
| 94 | |
| 95 | - Only sub-sets of DMA resources allocated in a static bank can be |
| 96 | registered in that bank using DMABuf_Register(); |
| 97 | If the DMABuf_Register() function is called for a static |
| 98 | bank then it must use allocator type 82 ('R') and the required memory |
| 99 | block must belong to an already allocated DMA resource in that bank; |
| 100 | |
| 101 | - The DMABuf_Register() function can be called for a static |
| 102 | bank also using allocator type 78 ('N') to register a DMA-unsafe buffer; |
| 103 | These DMA resources must be subsequently freed using the DMABuf_Release() |
| 104 | function; |
| 105 | |
| 106 | - An "all-pool" DMA resource of size (nr_of_blocks * block_size) can be |
| 107 | allocated in a static bank using DMABuf_Alloc() where nr_of_blocks |
| 108 | and block_size are compile-time configuration parameters |
| 109 | (see HWPAL_DMARESOURCE_BANKS in c_dmares_gen.h); |
| 110 | The DMABuf_Register() function can be used to register |
| 111 | sub-sets of this DMA resource; Only one such a all-pool DMA resource |
| 112 | can be allocated in one static bank and must be freed using |
| 113 | DMABuf_Release() function; |
| 114 | |
| 115 | - No other DMA resources can be allocated in a static bank |
| 116 | where an all-pool DMA resource is allocated. |
| 117 | |
| 118 | <end of document> |