dma.c revision eed34d0fc5e4b89269053ed855ef714edbcf4518 
1/* $Id: dma.c,v 1.7 1994/12/28 03:35:33 root Exp root $
2 * linux/kernel/dma.c: A DMA channel allocator. Inspired by linux/kernel/irq.c.
3 *
4 * Written by Hennus Bergman, 1992.
5 *
6 * 1994/12/26: Changes by Alex Nash to fix a minor bug in /proc/dma.
7 *   In the previous version the reported device could end up being wrong,
8 *   if a device requested a DMA channel that was already in use.
9 *   [It also happened to remove the sizeof(char *) == sizeof(int)
10 *   assumption introduced because of those /proc/dma patches. -- Hennus]
11 */
12#include <linux/module.h>
13#include <linux/kernel.h>
14#include <linux/errno.h>
15#include <linux/spinlock.h>
16#include <linux/string.h>
17#include <linux/seq_file.h>
18#include <linux/proc_fs.h>
19#include <linux/init.h>
20#include <asm/dma.h>
21#include <asm/system.h>
22
23
24
25/* A note on resource allocation:
26 *
27 * All drivers needing DMA channels, should allocate and release them
28 * through the public routines `request_dma()' and `free_dma()'.
29 *
30 * In order to avoid problems, all processes should allocate resources in
31 * the same sequence and release them in the reverse order.
32 *
33 * So, when allocating DMAs and IRQs, first allocate the IRQ, then the DMA.
34 * When releasing them, first release the DMA, then release the IRQ.
35 * If you don't, you may cause allocation requests to fail unnecessarily.
36 * This doesn't really matter now, but it will once we get real semaphores
37 * in the kernel.
38 */
39
40
41DEFINE_SPINLOCK(dma_spin_lock);
42
43/*
44 *	If our port doesn't define this it has no PC like DMA
45 */
46
47#ifdef MAX_DMA_CHANNELS
48
49
50/* Channel n is busy iff dma_chan_busy[n].lock != 0.
51 * DMA0 used to be reserved for DRAM refresh, but apparently not any more...
52 * DMA4 is reserved for cascading.
53 */
54
55struct dma_chan {
56	int  lock;
57	const char *device_id;
58};
59
60static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = {
61	[4] = { 1, "cascade" },
62};
63
64
65/**
66 * request_dma - request and reserve a system DMA channel
67 * @dmanr: DMA channel number
68 * @device_id: reserving device ID string, used in /proc/dma
69 */
70int request_dma(unsigned int dmanr, const char * device_id)
71{
72	if (dmanr >= MAX_DMA_CHANNELS)
73		return -EINVAL;
74
75	if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0)
76		return -EBUSY;
77
78	dma_chan_busy[dmanr].device_id = device_id;
79
80	/* old flag was 0, now contains 1 to indicate busy */
81	return 0;
82} /* request_dma */
83
84/**
85 * free_dma - free a reserved system DMA channel
86 * @dmanr: DMA channel number
87 */
88void free_dma(unsigned int dmanr)
89{
90	if (dmanr >= MAX_DMA_CHANNELS) {
91		printk(KERN_WARNING "Trying to free DMA%d\n", dmanr);
92		return;
93	}
94
95	if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) {
96		printk(KERN_WARNING "Trying to free free DMA%d\n", dmanr);
97		return;
98	}
99
100} /* free_dma */
101
102#else
103
104int request_dma(unsigned int dmanr, const char *device_id)
105{
106	return -EINVAL;
107}
108
109void free_dma(unsigned int dmanr)
110{
111}
112
113#endif
114
115#ifdef CONFIG_PROC_FS
116
117#ifdef MAX_DMA_CHANNELS
118static int proc_dma_show(struct seq_file *m, void *v)
119{
120	int i;
121
122	for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) {
123		if (dma_chan_busy[i].lock) {
124		    seq_printf(m, "%2d: %s\n", i,
125			       dma_chan_busy[i].device_id);
126		}
127	}
128	return 0;
129}
130#else
131static int proc_dma_show(struct seq_file *m, void *v)
132{
133	seq_puts(m, "No DMA\n");
134	return 0;
135}
136#endif /* MAX_DMA_CHANNELS */
137
138static int proc_dma_open(struct inode *inode, struct file *file)
139{
140	return single_open(file, proc_dma_show, NULL);
141}
142
143static struct file_operations proc_dma_operations = {
144	.open		= proc_dma_open,
145	.read		= seq_read,
146	.llseek		= seq_lseek,
147	.release	= single_release,
148};
149
150static int __init proc_dma_init(void)
151{
152	struct proc_dir_entry *e;
153
154	e = create_proc_entry("dma", 0, NULL);
155	if (e)
156		e->proc_fops = &proc_dma_operations;
157
158	return 0;
159}
160
161__initcall(proc_dma_init);
162#endif
163
164EXPORT_SYMBOL(request_dma);
165EXPORT_SYMBOL(free_dma);
166EXPORT_SYMBOL(dma_spin_lock);
167