linux/samples/kfifo/dma-example.c
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   1/*
   2 * Sample fifo dma implementation
   3 *
   4 * Copyright (C) 2010 Stefani Seibold <stefani@seibold.net>
   5 *
   6 * Released under the GPL version 2 only.
   7 *
   8 */
   9
  10#include <linux/init.h>
  11#include <linux/module.h>
  12#include <linux/kfifo.h>
  13
  14/*
  15 * This module shows how to handle fifo dma operations.
  16 */
  17
  18/* fifo size in elements (bytes) */
  19#define FIFO_SIZE       32
  20
  21static struct kfifo fifo;
  22
  23static int __init example_init(void)
  24{
  25        int                     i;
  26        unsigned int            ret;
  27        unsigned int            nents;
  28        struct scatterlist      sg[10];
  29
  30        printk(KERN_INFO "DMA fifo test start\n");
  31
  32        if (kfifo_alloc(&fifo, FIFO_SIZE, GFP_KERNEL)) {
  33                printk(KERN_WARNING "error kfifo_alloc\n");
  34                return -ENOMEM;
  35        }
  36
  37        printk(KERN_INFO "queue size: %u\n", kfifo_size(&fifo));
  38
  39        kfifo_in(&fifo, "test", 4);
  40
  41        for (i = 0; i != 9; i++)
  42                kfifo_put(&fifo, &i);
  43
  44        /* kick away first byte */
  45        kfifo_skip(&fifo);
  46
  47        printk(KERN_INFO "queue len: %u\n", kfifo_len(&fifo));
  48
  49        /*
  50         * Configure the kfifo buffer to receive data from DMA input.
  51         *
  52         *  .--------------------------------------.
  53         *  | 0 | 1 | 2 | ... | 12 | 13 | ... | 31 |
  54         *  |---|------------------|---------------|
  55         *   \_/ \________________/ \_____________/
  56         *    \          \                  \
  57         *     \          \_allocated data   \
  58         *      \_*free space*                \_*free space*
  59         *
  60         * We need two different SG entries: one for the free space area at the
  61         * end of the kfifo buffer (19 bytes) and another for the first free
  62         * byte at the beginning, after the kfifo_skip().
  63         */
  64        sg_init_table(sg, ARRAY_SIZE(sg));
  65        nents = kfifo_dma_in_prepare(&fifo, sg, ARRAY_SIZE(sg), FIFO_SIZE);
  66        printk(KERN_INFO "DMA sgl entries: %d\n", nents);
  67        if (!nents) {
  68                /* fifo is full and no sgl was created */
  69                printk(KERN_WARNING "error kfifo_dma_in_prepare\n");
  70                return -EIO;
  71        }
  72
  73        /* receive data */
  74        printk(KERN_INFO "scatterlist for receive:\n");
  75        for (i = 0; i < nents; i++) {
  76                printk(KERN_INFO
  77                "sg[%d] -> "
  78                "page_link 0x%.8lx offset 0x%.8x length 0x%.8x\n",
  79                        i, sg[i].page_link, sg[i].offset, sg[i].length);
  80
  81                if (sg_is_last(&sg[i]))
  82                        break;
  83        }
  84
  85        /* put here your code to setup and exectute the dma operation */
  86        /* ... */
  87
  88        /* example: zero bytes received */
  89        ret = 0;
  90
  91        /* finish the dma operation and update the received data */
  92        kfifo_dma_in_finish(&fifo, ret);
  93
  94        /* Prepare to transmit data, example: 8 bytes */
  95        nents = kfifo_dma_out_prepare(&fifo, sg, ARRAY_SIZE(sg), 8);
  96        printk(KERN_INFO "DMA sgl entries: %d\n", nents);
  97        if (!nents) {
  98                /* no data was available and no sgl was created */
  99                printk(KERN_WARNING "error kfifo_dma_out_prepare\n");
 100                return -EIO;
 101        }
 102
 103        printk(KERN_INFO "scatterlist for transmit:\n");
 104        for (i = 0; i < nents; i++) {
 105                printk(KERN_INFO
 106                "sg[%d] -> "
 107                "page_link 0x%.8lx offset 0x%.8x length 0x%.8x\n",
 108                        i, sg[i].page_link, sg[i].offset, sg[i].length);
 109
 110                if (sg_is_last(&sg[i]))
 111                        break;
 112        }
 113
 114        /* put here your code to setup and exectute the dma operation */
 115        /* ... */
 116
 117        /* example: 5 bytes transmitted */
 118        ret = 5;
 119
 120        /* finish the dma operation and update the transmitted data */
 121        kfifo_dma_out_finish(&fifo, ret);
 122
 123        ret = kfifo_len(&fifo);
 124        printk(KERN_INFO "queue len: %u\n", kfifo_len(&fifo));
 125
 126        if (ret != 7) {
 127                printk(KERN_WARNING "size mismatch: test failed");
 128                return -EIO;
 129        }
 130        printk(KERN_INFO "test passed\n");
 131
 132        return 0;
 133}
 134
 135static void __exit example_exit(void)
 136{
 137        kfifo_free(&fifo);
 138}
 139
 140module_init(example_init);
 141module_exit(example_exit);
 142MODULE_LICENSE("GPL");
 143MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
 144
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