// 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>");