1 | // SPDX-License-Identifier: GPL-2.0-only |
2 | /* |
3 | * Sample fifo dma implementation |
4 | * |
5 | * Copyright (C) 2010 Stefani Seibold <stefani@seibold.net> |
6 | */ |
7 | |
8 | #include <linux/init.h> |
9 | #include <linux/module.h> |
10 | #include <linux/kfifo.h> |
11 | |
12 | /* |
13 | * This module shows how to handle fifo dma operations. |
14 | */ |
15 | |
16 | /* fifo size in elements (bytes) */ |
17 | #define FIFO_SIZE 32 |
18 | |
19 | static struct kfifo fifo; |
20 | |
21 | static int __init example_init(void) |
22 | { |
23 | int i; |
24 | unsigned int ret; |
25 | unsigned int nents; |
26 | struct scatterlist sg[10]; |
27 | |
28 | printk(KERN_INFO "DMA fifo test start\n" ); |
29 | |
30 | if (kfifo_alloc(&fifo, FIFO_SIZE, GFP_KERNEL)) { |
31 | printk(KERN_WARNING "error kfifo_alloc\n" ); |
32 | return -ENOMEM; |
33 | } |
34 | |
35 | printk(KERN_INFO "queue size: %u\n" , kfifo_size(&fifo)); |
36 | |
37 | kfifo_in(&fifo, "test" , 4); |
38 | |
39 | for (i = 0; i != 9; i++) |
40 | kfifo_put(&fifo, i); |
41 | |
42 | /* kick away first byte */ |
43 | kfifo_skip(&fifo); |
44 | |
45 | printk(KERN_INFO "queue len: %u\n" , kfifo_len(&fifo)); |
46 | |
47 | /* |
48 | * Configure the kfifo buffer to receive data from DMA input. |
49 | * |
50 | * .--------------------------------------. |
51 | * | 0 | 1 | 2 | ... | 12 | 13 | ... | 31 | |
52 | * |---|------------------|---------------| |
53 | * \_/ \________________/ \_____________/ |
54 | * \ \ \ |
55 | * \ \_allocated data \ |
56 | * \_*free space* \_*free space* |
57 | * |
58 | * We need two different SG entries: one for the free space area at the |
59 | * end of the kfifo buffer (19 bytes) and another for the first free |
60 | * byte at the beginning, after the kfifo_skip(). |
61 | */ |
62 | sg_init_table(sg, ARRAY_SIZE(sg)); |
63 | nents = kfifo_dma_in_prepare(&fifo, sg, ARRAY_SIZE(sg), FIFO_SIZE); |
64 | printk(KERN_INFO "DMA sgl entries: %d\n" , nents); |
65 | if (!nents) { |
66 | /* fifo is full and no sgl was created */ |
67 | printk(KERN_WARNING "error kfifo_dma_in_prepare\n" ); |
68 | return -EIO; |
69 | } |
70 | |
71 | /* receive data */ |
72 | printk(KERN_INFO "scatterlist for receive:\n" ); |
73 | for (i = 0; i < nents; i++) { |
74 | printk(KERN_INFO |
75 | "sg[%d] -> " |
76 | "page %p offset 0x%.8x length 0x%.8x\n" , |
77 | i, sg_page(&sg[i]), sg[i].offset, sg[i].length); |
78 | |
79 | if (sg_is_last(sg: &sg[i])) |
80 | break; |
81 | } |
82 | |
83 | /* put here your code to setup and exectute the dma operation */ |
84 | /* ... */ |
85 | |
86 | /* example: zero bytes received */ |
87 | ret = 0; |
88 | |
89 | /* finish the dma operation and update the received data */ |
90 | kfifo_dma_in_finish(&fifo, ret); |
91 | |
92 | /* Prepare to transmit data, example: 8 bytes */ |
93 | nents = kfifo_dma_out_prepare(&fifo, sg, ARRAY_SIZE(sg), 8); |
94 | printk(KERN_INFO "DMA sgl entries: %d\n" , nents); |
95 | if (!nents) { |
96 | /* no data was available and no sgl was created */ |
97 | printk(KERN_WARNING "error kfifo_dma_out_prepare\n" ); |
98 | return -EIO; |
99 | } |
100 | |
101 | printk(KERN_INFO "scatterlist for transmit:\n" ); |
102 | for (i = 0; i < nents; i++) { |
103 | printk(KERN_INFO |
104 | "sg[%d] -> " |
105 | "page %p offset 0x%.8x length 0x%.8x\n" , |
106 | i, sg_page(&sg[i]), sg[i].offset, sg[i].length); |
107 | |
108 | if (sg_is_last(sg: &sg[i])) |
109 | break; |
110 | } |
111 | |
112 | /* put here your code to setup and exectute the dma operation */ |
113 | /* ... */ |
114 | |
115 | /* example: 5 bytes transmitted */ |
116 | ret = 5; |
117 | |
118 | /* finish the dma operation and update the transmitted data */ |
119 | kfifo_dma_out_finish(&fifo, ret); |
120 | |
121 | ret = kfifo_len(&fifo); |
122 | printk(KERN_INFO "queue len: %u\n" , kfifo_len(&fifo)); |
123 | |
124 | if (ret != 7) { |
125 | printk(KERN_WARNING "size mismatch: test failed" ); |
126 | return -EIO; |
127 | } |
128 | printk(KERN_INFO "test passed\n" ); |
129 | |
130 | return 0; |
131 | } |
132 | |
133 | static void __exit example_exit(void) |
134 | { |
135 | kfifo_free(&fifo); |
136 | } |
137 | |
138 | module_init(example_init); |
139 | module_exit(example_exit); |
140 | MODULE_LICENSE("GPL" ); |
141 | MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>" ); |
142 | |