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
19static struct kfifo fifo;
20
21static 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
133static void __exit example_exit(void)
134{
135	kfifo_free(&fifo);
136}
137
138module_init(example_init);
139module_exit(example_exit);
140MODULE_LICENSE("GPL");
141MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
142