xref: /openbmc/linux/samples/kfifo/dma-example.c (revision 8795a739)
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[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[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