dma-example.c

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/*
 * Sample fifo dma implementation
 *
 * Copyright (C) 2010 Stefani Seibold <[email protected]>
 *
 * Released under the GPL version 2 only.
 *
 */

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kfifo.h>

/*
 * This module shows how to handle fifo dma operations.
 */

/* fifo size in elements (bytes) */
#define FIFO_SIZE   32

static struct kfifo fifo;

static int __init example_init(void)
{
    int         i;
    unsigned int        ret;
    unsigned int        nents;
    struct scatterlist  sg[10];

    printk(KERN_INFO "DMA fifo test start\n");

    if (kfifo_alloc(&fifo, FIFO_SIZE, GFP_KERNEL)) {
        printk(KERN_WARNING "error kfifo_alloc\n");
        return -ENOMEM;
    }

    printk(KERN_INFO "queue size: %u\n", kfifo_size(&fifo));

    kfifo_in(&fifo, "test", 4);

    for (i = 0; i != 9; i++)
        kfifo_put(&fifo, &i);

    /* kick away first byte */
    kfifo_skip(&fifo);

    printk(KERN_INFO "queue len: %u\n", kfifo_len(&fifo));

    /*
     * Configure the kfifo buffer to receive data from DMA input.
     *
     *  .--------------------------------------.
     *  | 0 | 1 | 2 | ... | 12 | 13 | ... | 31 |
     *  |---|------------------|---------------|
     *   \_/ \________________/ \_____________/
     *    \          \                  \
     *     \          \_allocated data   \
     *      \_*free space*                \_*free space*
     *
     * We need two different SG entries: one for the free space area at the
     * end of the kfifo buffer (19 bytes) and another for the first free
     * byte at the beginning, after the kfifo_skip().
     */
    sg_init_table(sg, ARRAY_SIZE(sg));
    nents = kfifo_dma_in_prepare(&fifo, sg, ARRAY_SIZE(sg), FIFO_SIZE);
    printk(KERN_INFO "DMA sgl entries: %d\n", nents);
    if (!nents) {
        /* fifo is full and no sgl was created */
        printk(KERN_WARNING "error kfifo_dma_in_prepare\n");
        return -EIO;
    }

    /* receive data */
    printk(KERN_INFO "scatterlist for receive:\n");
    for (i = 0; i < nents; i++) {
        printk(KERN_INFO
        "sg[%d] -> "
        "page_link 0x%.8lx offset 0x%.8x length 0x%.8x\n",
            i, sg[i].page_link, sg[i].offset, sg[i].length);

        if (sg_is_last(&sg[i]))
            break;
    }

    /* put here your code to setup and exectute the dma operation */
    /* ... */

    /* example: zero bytes received */
    ret = 0;

    /* finish the dma operation and update the received data */
    kfifo_dma_in_finish(&fifo, ret);

    /* Prepare to transmit data, example: 8 bytes */
    nents = kfifo_dma_out_prepare(&fifo, sg, ARRAY_SIZE(sg), 8);
    printk(KERN_INFO "DMA sgl entries: %d\n", nents);
    if (!nents) {
        /* no data was available and no sgl was created */
        printk(KERN_WARNING "error kfifo_dma_out_prepare\n");
        return -EIO;
    }

    printk(KERN_INFO "scatterlist for transmit:\n");
    for (i = 0; i < nents; i++) {
        printk(KERN_INFO
        "sg[%d] -> "
        "page_link 0x%.8lx offset 0x%.8x length 0x%.8x\n",
            i, sg[i].page_link, sg[i].offset, sg[i].length);

        if (sg_is_last(&sg[i]))
            break;
    }

    /* put here your code to setup and exectute the dma operation */
    /* ... */

    /* example: 5 bytes transmitted */
    ret = 5;

    /* finish the dma operation and update the transmitted data */
    kfifo_dma_out_finish(&fifo, ret);

    ret = kfifo_len(&fifo);
    printk(KERN_INFO "queue len: %u\n", kfifo_len(&fifo));

    if (ret != 7) {
        printk(KERN_WARNING "size mismatch: test failed");
        return -EIO;
    }
    printk(KERN_INFO "test passed\n");

    return 0;
}

static void __exit example_exit(void)
{
    kfifo_free(&fifo);
}

module_init(example_init);
module_exit(example_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Stefani Seibold <[email protected]>");