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 20 static struct kfifo fifo; 21 22 static 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 } 133 134 static void __exit example_exit(void) 135 { 136 kfifo_free(&fifo); 137 } 138 139 module_init(example_init); 140 module_exit(example_exit); 141 MODULE_DESCRIPTION("Sample fifo dma implementation"); 142 MODULE_LICENSE("GPL"); 143 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>"); 144