LXR linux/samples/kfifo/dma-example.c

   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