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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/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 | /** |
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 | */ |
70 | int 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 | */ |
88 | void 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 | |
104 | int request_dma(unsigned int dmanr, const char *device_id) |
105 | { |
106 | return -EINVAL; |
107 | } |
108 | |
109 | void free_dma(unsigned int dmanr) |
110 | { |
111 | } |
112 | |
113 | #endif |
114 | |
115 | #ifdef CONFIG_PROC_FS |
116 | |
117 | #ifdef MAX_DMA_CHANNELS |
118 | static 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 |
131 | static 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 | |
138 | static int proc_dma_open(struct inode *inode, struct file *file) |
139 | { |
140 | return single_open(file, proc_dma_show, NULL); |
141 | } |
142 | |
143 | static const 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 | |
150 | static int __init proc_dma_init(void) |
151 | { |
152 | proc_create("dma", 0, NULL, &proc_dma_operations); |
153 | return 0; |
154 | } |
155 | |
156 | __initcall(proc_dma_init); |
157 | #endif |
158 | |
159 | EXPORT_SYMBOL(request_dma); |
160 | EXPORT_SYMBOL(free_dma); |
161 | EXPORT_SYMBOL(dma_spin_lock); |
162 |
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