Root/samples/kfifo/dma-example.c

1/*
2 * Sample fifo dma implementation
3 *
4 * Copyright (C) 2010 Stefani Seibold <stefani@seibold.net>
5 *
6 * Released under the GPL version 2 only.
7 *
8 */
9
10#include <linux/init.h>
11#include <linux/module.h>
12#include <linux/kfifo.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_link 0x%.8lx offset 0x%.8x length 0x%.8x\n",
79            i, sg[i].page_link, 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_link 0x%.8lx offset 0x%.8x length 0x%.8x\n",
108            i, sg[i].page_link, 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_LICENSE("GPL");
143MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
144

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