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1// SPDX-License-Identifier: GPL-2.0-only2/*3 * Sample fifo dma implementation4 *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 3219 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 the60 * end of the kfifo buffer (19 bytes) and another for the first free61 * 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_INFO76 "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_INFO105 "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_DESCRIPTION("Sample fifo dma implementation");142MODULE_LICENSE("GPL");143MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");144