498d319bb5
This patch enhances the type safety for the kfifo API. It is now safe to put const data into a non const FIFO and the API will now generate a compiler warning when reading from the fifo where the destination address is pointing to a const variable. As a side effect the kfifo_put() does now expect the value of an element instead a pointer to the element. This was suggested Russell King. It make the handling of the kfifo_put easier since there is no need to create a helper variable for getting the address of a pointer or to pass integers of different sizes. IMHO the API break is okay, since there are currently only six users of kfifo_put(). The code is also cleaner by kicking out the "if (0)" expressions. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Stefani Seibold <stefani@seibold.net> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Hauke Mehrtens <hauke@hauke-m.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
143 lines
3.4 KiB
C
143 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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