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1 /*
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/export.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 
22 
23 
24 /* A note on resource allocation:
25  *
26  * All drivers needing DMA channels, should allocate and release them
27  * through the public routines `request_dma()' and `free_dma()'.
28  *
29  * In order to avoid problems, all processes should allocate resources in
30  * the same sequence and release them in the reverse order.
31  *
32  * So, when allocating DMAs and IRQs, first allocate the IRQ, then the DMA.
33  * When releasing them, first release the DMA, then release the IRQ.
34  * If you don't, you may cause allocation requests to fail unnecessarily.
35  * This doesn't really matter now, but it will once we get real semaphores
36  * in the kernel.
37  */
38 
39 
40 DEFINE_SPINLOCK(dma_spin_lock);
41 
42 /*
43  *	If our port doesn't define this it has no PC like DMA
44  */
45 
46 #ifdef MAX_DMA_CHANNELS
47 
48 
49 /* Channel n is busy iff dma_chan_busy[n].lock != 0.
50  * DMA0 used to be reserved for DRAM refresh, but apparently not any more...
51  * DMA4 is reserved for cascading.
52  */
53 
54 struct dma_chan {
55 	int  lock;
56 	const char *device_id;
57 };
58 
59 static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = {
60 	[4] = { 1, "cascade" },
61 };
62 
63 
64 /**
65  * request_dma - request and reserve a system DMA channel
66  * @dmanr: DMA channel number
67  * @device_id: reserving device ID string, used in /proc/dma
68  */
request_dma(unsigned int dmanr,const char * device_id)69 int request_dma(unsigned int dmanr, const char * device_id)
70 {
71 	if (dmanr >= MAX_DMA_CHANNELS)
72 		return -EINVAL;
73 
74 	if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0)
75 		return -EBUSY;
76 
77 	dma_chan_busy[dmanr].device_id = device_id;
78 
79 	/* old flag was 0, now contains 1 to indicate busy */
80 	return 0;
81 } /* request_dma */
82 
83 /**
84  * free_dma - free a reserved system DMA channel
85  * @dmanr: DMA channel number
86  */
free_dma(unsigned int dmanr)87 void free_dma(unsigned int dmanr)
88 {
89 	if (dmanr >= MAX_DMA_CHANNELS) {
90 		printk(KERN_WARNING "Trying to free DMA%d\n", dmanr);
91 		return;
92 	}
93 
94 	if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) {
95 		printk(KERN_WARNING "Trying to free free DMA%d\n", dmanr);
96 		return;
97 	}
98 
99 } /* free_dma */
100 
101 #else
102 
request_dma(unsigned int dmanr,const char * device_id)103 int request_dma(unsigned int dmanr, const char *device_id)
104 {
105 	return -EINVAL;
106 }
107 
free_dma(unsigned int dmanr)108 void free_dma(unsigned int dmanr)
109 {
110 }
111 
112 #endif
113 
114 #ifdef CONFIG_PROC_FS
115 
116 #ifdef MAX_DMA_CHANNELS
proc_dma_show(struct seq_file * m,void * v)117 static int proc_dma_show(struct seq_file *m, void *v)
118 {
119 	int i;
120 
121 	for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) {
122 		if (dma_chan_busy[i].lock) {
123 			seq_printf(m, "%2d: %s\n", i,
124 				   dma_chan_busy[i].device_id);
125 		}
126 	}
127 	return 0;
128 }
129 #else
proc_dma_show(struct seq_file * m,void * v)130 static int proc_dma_show(struct seq_file *m, void *v)
131 {
132 	seq_puts(m, "No DMA\n");
133 	return 0;
134 }
135 #endif /* MAX_DMA_CHANNELS */
136 
proc_dma_open(struct inode * inode,struct file * file)137 static int proc_dma_open(struct inode *inode, struct file *file)
138 {
139 	return single_open(file, proc_dma_show, NULL);
140 }
141 
142 static const struct file_operations proc_dma_operations = {
143 	.open		= proc_dma_open,
144 	.read		= seq_read,
145 	.llseek		= seq_lseek,
146 	.release	= single_release,
147 };
148 
proc_dma_init(void)149 static int __init proc_dma_init(void)
150 {
151 	proc_create("dma", 0, NULL, &proc_dma_operations);
152 	return 0;
153 }
154 
155 __initcall(proc_dma_init);
156 #endif
157 
158 EXPORT_SYMBOL(request_dma);
159 EXPORT_SYMBOL(free_dma);
160 EXPORT_SYMBOL(dma_spin_lock);
161