xref: /openbmc/linux/kernel/dma.c (revision d5cb9783536a41df9f9cba5b0a1d78047ed787f7)
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 
41 DEFINE_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 
55 struct dma_chan {
56 	int  lock;
57 	const char *device_id;
58 };
59 
60 static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = {
61 	[4] = { 1, "cascade" },
62 };
63 
64 
65 int request_dma(unsigned int dmanr, const char * device_id)
66 {
67 	if (dmanr >= MAX_DMA_CHANNELS)
68 		return -EINVAL;
69 
70 	if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0)
71 		return -EBUSY;
72 
73 	dma_chan_busy[dmanr].device_id = device_id;
74 
75 	/* old flag was 0, now contains 1 to indicate busy */
76 	return 0;
77 } /* request_dma */
78 
79 
80 void free_dma(unsigned int dmanr)
81 {
82 	if (dmanr >= MAX_DMA_CHANNELS) {
83 		printk(KERN_WARNING "Trying to free DMA%d\n", dmanr);
84 		return;
85 	}
86 
87 	if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) {
88 		printk(KERN_WARNING "Trying to free free DMA%d\n", dmanr);
89 		return;
90 	}
91 
92 } /* free_dma */
93 
94 #else
95 
96 int request_dma(unsigned int dmanr, const char *device_id)
97 {
98 	return -EINVAL;
99 }
100 
101 void free_dma(unsigned int dmanr)
102 {
103 }
104 
105 #endif
106 
107 #ifdef CONFIG_PROC_FS
108 
109 #ifdef MAX_DMA_CHANNELS
110 static int proc_dma_show(struct seq_file *m, void *v)
111 {
112 	int i;
113 
114 	for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) {
115 		if (dma_chan_busy[i].lock) {
116 		    seq_printf(m, "%2d: %s\n", i,
117 			       dma_chan_busy[i].device_id);
118 		}
119 	}
120 	return 0;
121 }
122 #else
123 static int proc_dma_show(struct seq_file *m, void *v)
124 {
125 	seq_puts(m, "No DMA\n");
126 	return 0;
127 }
128 #endif /* MAX_DMA_CHANNELS */
129 
130 static int proc_dma_open(struct inode *inode, struct file *file)
131 {
132 	return single_open(file, proc_dma_show, NULL);
133 }
134 
135 static struct file_operations proc_dma_operations = {
136 	.open		= proc_dma_open,
137 	.read		= seq_read,
138 	.llseek		= seq_lseek,
139 	.release	= single_release,
140 };
141 
142 static int __init proc_dma_init(void)
143 {
144 	struct proc_dir_entry *e;
145 
146 	e = create_proc_entry("dma", 0, NULL);
147 	if (e)
148 		e->proc_fops = &proc_dma_operations;
149 
150 	return 0;
151 }
152 
153 __initcall(proc_dma_init);
154 #endif
155 
156 EXPORT_SYMBOL(request_dma);
157 EXPORT_SYMBOL(free_dma);
158 EXPORT_SYMBOL(dma_spin_lock);
159