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/kfifo.h>
10 #include <linux/module.h>
11 #include <linux/scatterlist.h>
12
13 /*
14 * This module shows how to handle fifo dma operations.
15 */
16
17 /* fifo size in elements (bytes) */
18 #define FIFO_SIZE 32
19
20 static struct kfifo fifo;
21
22 static int __init example_init(void)
23 {
24 int i;
25 unsigned int ret;
26 unsigned int nents;
27 struct scatterlist sg[10];
28
29 printk(KERN_INFO "DMA fifo test start\n");
30
31 if (kfifo_alloc(&fifo, FIFO_SIZE, GFP_KERNEL)) {
32 printk(KERN_WARNING "error kfifo_alloc\n");
33 return -ENOMEM;
34 }
35
36 printk(KERN_INFO "queue size: %u\n", kfifo_size(&fifo));
37
38 kfifo_in(&fifo, "test", 4);
39
40 for (i = 0; i != 9; i++)
41 kfifo_put(&fifo, i);
42
43 /* kick away first byte */
44 kfifo_skip(&fifo);
45
46 printk(KERN_INFO "queue len: %u\n", kfifo_len(&fifo));
47
48 /*
49 * Configure the kfifo buffer to receive data from DMA input.
50 *
51 * .--------------------------------------.
52 * | 0 | 1 | 2 | ... | 12 | 13 | ... | 31 |
53 * |---|------------------|---------------|
54 * \_/ \________________/ \_____________/
55 * \ \ \
56 * \ \_allocated data \
57 * \_*free space* \_*free space*
58 *
59 * We need two different SG entries: one for the free space area at the
60 * end of the kfifo buffer (19 bytes) and another for the first free
61 * byte at the beginning, after the kfifo_skip().
62 */
63 sg_init_table(sg, ARRAY_SIZE(sg));
64 nents = kfifo_dma_in_prepare(&fifo, sg, ARRAY_SIZE(sg), FIFO_SIZE);
65 printk(KERN_INFO "DMA sgl entries: %d\n", nents);
66 if (!nents) {
67 /* fifo is full and no sgl was created */
68 printk(KERN_WARNING "error kfifo_dma_in_prepare\n");
69 return -EIO;
70 }
71
72 /* receive data */
73 printk(KERN_INFO "scatterlist for receive:\n");
74 for (i = 0; i < nents; i++) {
75 printk(KERN_INFO
76 "sg[%d] -> "
77 "page %p offset 0x%.8x length 0x%.8x\n",
78 i, sg_page(&sg[i]), sg[i].offset, sg[i].length);
79
80 if (sg_is_last(&sg[i]))
81 break;
82 }
83
84 /* put here your code to setup and exectute the dma operation */
85 /* ... */
86
87 /* example: zero bytes received */
88 ret = 0;
89
90 /* finish the dma operation and update the received data */
91 kfifo_dma_in_finish(&fifo, ret);
92
93 /* Prepare to transmit data, example: 8 bytes */
94 nents = kfifo_dma_out_prepare(&fifo, sg, ARRAY_SIZE(sg), 8);
95 printk(KERN_INFO "DMA sgl entries: %d\n", nents);
96 if (!nents) {
97 /* no data was available and no sgl was created */
98 printk(KERN_WARNING "error kfifo_dma_out_prepare\n");
99 return -EIO;
100 }
101
102 printk(KERN_INFO "scatterlist for transmit:\n");
103 for (i = 0; i < nents; i++) {
104 printk(KERN_INFO
105 "sg[%d] -> "
106 "page %p offset 0x%.8x length 0x%.8x\n",
107 i, sg_page(&sg[i]), sg[i].offset, sg[i].length);
108
109 if (sg_is_last(&sg[i]))
110 break;
111 }
112
113 /* put here your code to setup and exectute the dma operation */
114 /* ... */
115
116 /* example: 5 bytes transmitted */
117 ret = 5;
118
119 /* finish the dma operation and update the transmitted data */
120 kfifo_dma_out_finish(&fifo, ret);
121
122 ret = kfifo_len(&fifo);
123 printk(KERN_INFO "queue len: %u\n", kfifo_len(&fifo));
124
125 if (ret != 7) {
126 printk(KERN_WARNING "size mismatch: test failed");
127 return -EIO;
128 }
129 printk(KERN_INFO "test passed\n");
130
131 return 0;
132 }
133
134 static void __exit example_exit(void)
135 {
136 kfifo_free(&fifo);
137 }
138
139 module_init(example_init);
140 module_exit(example_exit);
141 MODULE_DESCRIPTION("Sample fifo dma implementation");
142 MODULE_LICENSE("GPL");
143 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
144
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