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