142 lines
3.4 KiB
C
142 lines
3.4 KiB
C
// 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/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 %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_LICENSE("GPL");
|
|
MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
|