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