399f1e30ac
The kfifo_dma family of functions use sg_mark_end() on the last element in their scatterlist. This forces use of a fresh scatterlist for each DMA operation, which makes recycling a single scatterlist impossible. Change the behavior of the kfifo_dma functions to match the usage of the dma_map_sg function. This means that users must respect the returned nents value. The sample code is updated to reflect the change. This bug is trivial to cause: call kfifo_dma_in_prepare() such that it prepares a scatterlist with a single entry comprising the whole fifo. This is the case when you map the entirety of a newly created empty fifo. This causes the setup_sgl() function to mark the first scatterlist entry as the end of the chain, no matter what comes after it. Afterwards, add and remove some data from the fifo such that another call to kfifo_dma_in_prepare() will create two scatterlist entries. It returns nents=2. However, due to the previous sg_mark_end() call, sg_is_last() will now return true for the first scatterlist element. This causes the sample code to print a single scatterlist element when it should print two. By removing the call to sg_mark_end(), we make the API as similar as possible to the DMA mapping API. All users are required to respect the returned nents. Signed-off-by: Ira W. Snyder <iws@ovro.caltech.edu> Cc: Stefani Seibold <stefani@seibold.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
144 lines
3.4 KiB
C
144 lines
3.4 KiB
C
/*
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* Sample fifo dma implementation
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*
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* Copyright (C) 2010 Stefani Seibold <stefani@seibold.net>
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*
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* Released under the GPL version 2 only.
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*
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*/
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#include <linux/init.h>
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#include <linux/module.h>
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#include <linux/kfifo.h>
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/*
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* This module shows how to handle fifo dma operations.
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*/
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/* fifo size in elements (bytes) */
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#define FIFO_SIZE 32
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static struct kfifo fifo;
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static int __init example_init(void)
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{
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int i;
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unsigned int ret;
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unsigned int nents;
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struct scatterlist sg[10];
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printk(KERN_INFO "DMA fifo test start\n");
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if (kfifo_alloc(&fifo, FIFO_SIZE, GFP_KERNEL)) {
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printk(KERN_WARNING "error kfifo_alloc\n");
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return -ENOMEM;
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}
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printk(KERN_INFO "queue size: %u\n", kfifo_size(&fifo));
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kfifo_in(&fifo, "test", 4);
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for (i = 0; i != 9; i++)
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kfifo_put(&fifo, &i);
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/* kick away first byte */
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kfifo_skip(&fifo);
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printk(KERN_INFO "queue len: %u\n", kfifo_len(&fifo));
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/*
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* Configure the kfifo buffer to receive data from DMA input.
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*
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* .--------------------------------------.
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* | 0 | 1 | 2 | ... | 12 | 13 | ... | 31 |
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* |---|------------------|---------------|
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* \_/ \________________/ \_____________/
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* \ \ \
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* \ \_allocated data \
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* \_*free space* \_*free space*
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*
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* We need two different SG entries: one for the free space area at the
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* end of the kfifo buffer (19 bytes) and another for the first free
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* byte at the beginning, after the kfifo_skip().
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*/
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sg_init_table(sg, ARRAY_SIZE(sg));
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nents = kfifo_dma_in_prepare(&fifo, sg, ARRAY_SIZE(sg), FIFO_SIZE);
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printk(KERN_INFO "DMA sgl entries: %d\n", nents);
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if (!nents) {
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/* fifo is full and no sgl was created */
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printk(KERN_WARNING "error kfifo_dma_in_prepare\n");
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return -EIO;
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}
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/* receive data */
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printk(KERN_INFO "scatterlist for receive:\n");
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for (i = 0; i < nents; i++) {
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printk(KERN_INFO
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"sg[%d] -> "
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"page_link 0x%.8lx offset 0x%.8x length 0x%.8x\n",
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i, sg[i].page_link, sg[i].offset, sg[i].length);
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if (sg_is_last(&sg[i]))
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break;
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}
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/* put here your code to setup and exectute the dma operation */
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/* ... */
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/* example: zero bytes received */
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ret = 0;
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/* finish the dma operation and update the received data */
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kfifo_dma_in_finish(&fifo, ret);
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/* Prepare to transmit data, example: 8 bytes */
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nents = kfifo_dma_out_prepare(&fifo, sg, ARRAY_SIZE(sg), 8);
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printk(KERN_INFO "DMA sgl entries: %d\n", nents);
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if (!nents) {
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/* no data was available and no sgl was created */
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printk(KERN_WARNING "error kfifo_dma_out_prepare\n");
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return -EIO;
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}
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printk(KERN_INFO "scatterlist for transmit:\n");
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for (i = 0; i < nents; i++) {
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printk(KERN_INFO
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"sg[%d] -> "
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"page_link 0x%.8lx offset 0x%.8x length 0x%.8x\n",
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i, sg[i].page_link, sg[i].offset, sg[i].length);
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if (sg_is_last(&sg[i]))
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break;
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}
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/* put here your code to setup and exectute the dma operation */
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/* ... */
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/* example: 5 bytes transmitted */
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ret = 5;
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/* finish the dma operation and update the transmitted data */
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kfifo_dma_out_finish(&fifo, ret);
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ret = kfifo_len(&fifo);
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printk(KERN_INFO "queue len: %u\n", kfifo_len(&fifo));
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if (ret != 7) {
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printk(KERN_WARNING "size mismatch: test failed");
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return -EIO;
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}
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printk(KERN_INFO "test passed\n");
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return 0;
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}
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static void __exit example_exit(void)
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{
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kfifo_free(&fifo);
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}
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module_init(example_init);
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module_exit(example_exit);
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>");
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