// SPDX-License-Identifier: GPL-2.0-only
/*
 * Sample fifo dma implementation
 *
 * Copyright (C) 2010 Stefani Seibold <stefani@seibold.net>
 */

#include <linux/init.h>
#include <linux/kfifo.h>
#include <linux/module.h>
#include <linux/scatterlist.h>
#include <linux/dma-mapping.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 %p offset 0x%.8x length 0x%.8x\n",
                        i, sg_page(&sg[i]), 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 %p offset 0x%.8x length 0x%.8x\n",
                        i, sg_page(&sg[i]), 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_DESCRIPTION("Sample fifo dma implementation");
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");