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