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/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       32
  19
  20 static struct kfifo fifo;
  21
  22 static 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 the
  60          * end of the kfifo buffer (19 bytes) and another for the first free
  61          * 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_INFO
  76                 "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_INFO
 105                 "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
 134 static void __exit example_exit(void)
 135 {
 136         kfifo_free(&fifo);
 137 }
 138
 139 module_init(example_init);
 140 module_exit(example_exit);
 141 MODULE_DESCRIPTION("Sample fifo dma implementation");
 142 MODULE_LICENSE("GPL");
 143 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");