samples/kfifo/dma-example.c

   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
  21 static struct kfifo fifo;
  22
  23 static 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 %p offset 0x%.8x length 0x%.8x\n",
  79                         i, sg_page(&sg[i]), 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 %p offset 0x%.8x length 0x%.8x\n",
 108                         i, sg_page(&sg[i]), 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
 135 static void __exit example_exit(void)
 136 {
 137         kfifo_free(&fifo);
 138 }
 139
 140 module_init(example_init);
 141 module_exit(example_exit);
 142 MODULE_LICENSE("GPL");
 143 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");