/* $Id: dma.c,v 1.7 1994/12/28 03:35:33 root Exp root $ * linux/kernel/dma.c: A DMA channel allocator. Inspired by linux/kernel/irq.c. * * Written by Hennus Bergman, 1992. * * 1994/12/26: Changes by Alex Nash to fix a minor bug in /proc/dma. *   In the previous version the reported device could end up being wrong, *   if a device requested a DMA channel that was already in use. *   [It also happened to remove the sizeof(char *) == sizeof(int) *   assumption introduced because of those /proc/dma patches. -- Hennus] */#include <linux/module.h>#include <linux/kernel.h>#include <linux/errno.h>#include <linux/spinlock.h>#include <linux/string.h>#include <linux/seq_file.h>#include <linux/proc_fs.h>#include <linux/init.h>#include <asm/dma.h>#include <asm/system.h>/* A note on resource allocation: * * All drivers needing DMA channels, should allocate and release them * through the public routines `request_dma()' and `free_dma()'. * * In order to avoid problems, all processes should allocate resources in * the same sequence and release them in the reverse order. * * So, when allocating DMAs and IRQs, first allocate the IRQ, then the DMA. * When releasing them, first release the DMA, then release the IRQ. * If you don't, you may cause allocation requests to fail unnecessarily. * This doesn't really matter now, but it will once we get real semaphores * in the kernel. */DEFINE_SPINLOCK(dma_spin_lock);/* *	If our port doesn't define this it has no PC like DMA */#ifdef MAX_DMA_CHANNELS/* Channel n is busy iff dma_chan_busy[n].lock != 0. * DMA0 used to be reserved for DRAM refresh, but apparently not any more... * DMA4 is reserved for cascading. */struct dma_chan {	int  lock;	const char *device_id;};static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = {	[4] = { 1, "cascade" },};/** * request_dma - request and reserve a system DMA channel * @dmanr: DMA channel number * @device_id: reserving device ID string, used in /proc/dma */int request_dma(unsigned int dmanr, const char * device_id){	if (dmanr >= MAX_DMA_CHANNELS)		return -EINVAL;	if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0)		return -EBUSY;	dma_chan_busy[dmanr].device_id = device_id;	/* old flag was 0, now contains 1 to indicate busy */	return 0;} /* request_dma *//** * free_dma - free a reserved system DMA channel * @dmanr: DMA channel number */void free_dma(unsigned int dmanr){	if (dmanr >= MAX_DMA_CHANNELS) {		printk(KERN_WARNING "Trying to free DMA%d\n", dmanr);		return;	}	if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) {		printk(KERN_WARNING "Trying to free free DMA%d\n", dmanr);		return;	}} /* free_dma */#elseint request_dma(unsigned int dmanr, const char *device_id){	return -EINVAL;}void free_dma(unsigned int dmanr){}#endif#ifdef CONFIG_PROC_FS#ifdef MAX_DMA_CHANNELSstatic int proc_dma_show(struct seq_file *m, void *v){	int i;	for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) {		if (dma_chan_busy[i].lock) {			seq_printf(m, "%2d: %s\n", i,				   dma_chan_busy[i].device_id);		}	}	return 0;}#elsestatic int proc_dma_show(struct seq_file *m, void *v){	seq_puts(m, "No DMA\n");	return 0;}#endif /* MAX_DMA_CHANNELS */static int proc_dma_open(struct inode *inode, struct file *file){	return single_open(file, proc_dma_show, NULL);}static const struct file_operations proc_dma_operations = {	.open		= proc_dma_open,	.read		= seq_read,	.llseek		= seq_lseek,	.release	= single_release,};static int __init proc_dma_init(void){	proc_create("dma", 0, NULL, &proc_dma_operations);	return 0;}__initcall(proc_dma_init);#endifEXPORT_SYMBOL(request_dma);EXPORT_SYMBOL(free_dma);EXPORT_SYMBOL(dma_spin_lock);