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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Sample fifo dma implementation
4 *
5 * Copyright (C) 2010 Stefani Seibold <[email protected]>
6 */
7
8#include <linux/init.h>
9#include <linux/kfifo.h>
10#include <linux/module.h>
11#include <linux/scatterlist.h>
12#include <linux/dma-mapping.h>
13
14/*
15 * This module shows how to handle fifo dma operations.
16 */
17
18/* fifo size in elements (bytes) */
19#define FIFO_SIZE 32
20
21static struct kfifo fifo;
22
23static int __init example_init(void)
24{
25 int i;
26 unsigned int ret;
27 unsigned int nents;
28 struct scatterlist sg[10];
29
30 printk(KERN_INFO "DMA fifo test start\n");
31
32 if (kfifo_alloc(&fifo, FIFO_SIZE, GFP_KERNEL)) {
33 printk(KERN_WARNING "error kfifo_alloc\n");
34 return -ENOMEM;
35 }
36
37 printk(KERN_INFO "queue size: %u\n", kfifo_size(&fifo));
38
39 kfifo_in(&fifo, "test", 4);
40
41 for (i = 0; i != 9; i++)
42 kfifo_put(&fifo, i);
43
44 /* kick away first byte */
45 kfifo_skip(&fifo);
46
47 printk(KERN_INFO "queue len: %u\n", kfifo_len(&fifo));
48
49 /*
50 * Configure the kfifo buffer to receive data from DMA input.
51 *
52 * .--------------------------------------.
53 * | 0 | 1 | 2 | ... | 12 | 13 | ... | 31 |
54 * |---|------------------|---------------|
55 * \_/ \________________/ \_____________/
56 * \ \ \
57 * \ \_allocated data \
58 * \_*free space* \_*free space*
59 *
60 * We need two different SG entries: one for the free space area at the
61 * end of the kfifo buffer (19 bytes) and another for the first free
62 * byte at the beginning, after the kfifo_skip().
63 */
64 sg_init_table(sg, ARRAY_SIZE(sg));
65 nents = kfifo_dma_in_prepare(&fifo, sg, ARRAY_SIZE(sg), FIFO_SIZE);
66 printk(KERN_INFO "DMA sgl entries: %d\n", nents);
67 if (!nents) {
68 /* fifo is full and no sgl was created */
69 printk(KERN_WARNING "error kfifo_dma_in_prepare\n");
70 return -EIO;
71 }
72
73 /* receive data */
74 printk(KERN_INFO "scatterlist for receive:\n");
75 for (i = 0; i < nents; i++) {
76 printk(KERN_INFO
77 "sg[%d] -> "
78 "page %p offset 0x%.8x length 0x%.8x\n",
79 i, sg_page(&sg[i]), sg[i].offset, sg[i].length);
80
81 if (sg_is_last(&sg[i]))
82 break;
83 }
84
85 /* put here your code to setup and exectute the dma operation */
86 /* ... */
87
88 /* example: zero bytes received */
89 ret = 0;
90
91 /* finish the dma operation and update the received data */
92 kfifo_dma_in_finish(&fifo, ret);
93
94 /* Prepare to transmit data, example: 8 bytes */
95 nents = kfifo_dma_out_prepare(&fifo, sg, ARRAY_SIZE(sg), 8);
96 printk(KERN_INFO "DMA sgl entries: %d\n", nents);
97 if (!nents) {
98 /* no data was available and no sgl was created */
99 printk(KERN_WARNING "error kfifo_dma_out_prepare\n");
100 return -EIO;
101 }
102
103 printk(KERN_INFO "scatterlist for transmit:\n");
104 for (i = 0; i < nents; i++) {
105 printk(KERN_INFO
106 "sg[%d] -> "
107 "page %p offset 0x%.8x length 0x%.8x\n",
108 i, sg_page(&sg[i]), sg[i].offset, sg[i].length);
109
110 if (sg_is_last(&sg[i]))
111 break;
112 }
113
114 /* put here your code to setup and exectute the dma operation */
115 /* ... */
116
117 /* example: 5 bytes transmitted */
118 ret = 5;
119
120 /* finish the dma operation and update the transmitted data */
121 kfifo_dma_out_finish(&fifo, ret);
122
123 ret = kfifo_len(&fifo);
124 printk(KERN_INFO "queue len: %u\n", kfifo_len(&fifo));
125
126 if (ret != 7) {
127 printk(KERN_WARNING "size mismatch: test failed");
128 return -EIO;
129 }
130 printk(KERN_INFO "test passed\n");
131
132 return 0;
133}
134
135static void __exit example_exit(void)
136{
137 kfifo_free(&fifo);
138}
139
140module_init(example_init);
141module_exit(example_exit);
142MODULE_DESCRIPTION("Sample fifo dma implementation");
143MODULE_LICENSE("GPL");
144MODULE_AUTHOR("Stefani Seibold <[email protected]>");