linux/samples/kfifo/dma-example.c

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/*
* Sample fifo dma implementation
*
* Copyright (C) 2010 Stefani Seibold <stefani@seibold.net>
*
* 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;
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().
*/
kfifo: fix kernel BUG in dma example The scatterlist is used uninitialized in kfifo_dma_in_prepare(). This triggers the following bug if CONFIG_DEBUG_SG=y: ------------[ cut here ]------------ kernel BUG at include/linux/scatterlist.h:65! invalid opcode: 0000 [#1] PREEMPT SMP ... Call Trace: [<ffffffff810a1eab>] setup_sgl+0x6b/0xe0 [<ffffffffa03d7000>] ? example_init+0x0/0x265 [dma_example] [<ffffffff810a2021>] __kfifo_dma_in_prepare+0x21/0x30 [<ffffffffa03d7124>] example_init+0x124/0x265 [dma_example] [<ffffffff810f9c55>] ? trace_module_notify+0x25/0x370 [<ffffffff81110c6e>] ? free_pages_prepare+0x11e/0x1e0 [<ffffffff8106f2b1>] ? get_parent_ip+0x11/0x50 [<ffffffff810f9c55>] ? trace_module_notify+0x25/0x370 [<ffffffff810b65fd>] ? trace_hardirqs_on+0xd/0x10 [<ffffffff814beade>] ? mutex_unlock+0xe/0x10 [<ffffffff810f9c71>] ? trace_module_notify+0x41/0x370 [<ffffffff810a77d5>] ? __blocking_notifier_call_chain+0x45/0x80 [<ffffffff81137b7a>] ? vfree+0x2a/0x30 [<ffffffff810a6ac3>] ? up_read+0x23/0x40 [<ffffffff810a77f5>] ? __blocking_notifier_call_chain+0x65/0x80 [<ffffffff810001e3>] do_one_initcall+0x43/0x180 [<ffffffff810c577a>] sys_init_module+0xba/0x200 [<ffffffff8103819b>] system_call_fastpath+0x16/0x1b RIP [<ffffffff810a1e31>] setup_sgl_buf+0x1a1/0x1b0 RSP <ffff88006720dc98> ---[ end trace a72b979fd3c1d3a5 ]--- Add the proper initialization to avoid the bug. Signed-off-by: Andrea Righi <arighi@develer.com> Acked-by: Stefani Seibold <stefani@seibold.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-08-19 21:13:29 +00:00
sg_init_table(sg, ARRAY_SIZE(sg));
ret = kfifo_dma_in_prepare(&fifo, sg, ARRAY_SIZE(sg), FIFO_SIZE);
printk(KERN_INFO "DMA sgl entries: %d\n", ret);
if (!ret) {
/* 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 < ARRAY_SIZE(sg); 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 */
ret = kfifo_dma_out_prepare(&fifo, sg, ARRAY_SIZE(sg), 8);
printk(KERN_INFO "DMA sgl entries: %d\n", ret);
if (!ret) {
/* 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 < ARRAY_SIZE(sg); 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 <stefani@seibold.net>");