File: /usr/src/linux/kernel/dma.c
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
13 #include <linux/kernel.h>
14 #include <linux/errno.h>
15 #include <linux/spinlock.h>
16 #include <linux/string.h>
17 #include <asm/dma.h>
18 #include <asm/system.h>
19
20
21
22 /* A note on resource allocation:
23 *
24 * All drivers needing DMA channels, should allocate and release them
25 * through the public routines `request_dma()' and `free_dma()'.
26 *
27 * In order to avoid problems, all processes should allocate resources in
28 * the same sequence and release them in the reverse order.
29 *
30 * So, when allocating DMAs and IRQs, first allocate the IRQ, then the DMA.
31 * When releasing them, first release the DMA, then release the IRQ.
32 * If you don't, you may cause allocation requests to fail unnecessarily.
33 * This doesn't really matter now, but it will once we get real semaphores
34 * in the kernel.
35 */
36
37
38 spinlock_t dma_spin_lock = SPIN_LOCK_UNLOCKED;
39
40 /*
41 * If our port doesn't define this it has no PC like DMA
42 */
43
44 #ifdef MAX_DMA_CHANNELS
45
46
47 /* Channel n is busy iff dma_chan_busy[n].lock != 0.
48 * DMA0 used to be reserved for DRAM refresh, but apparently not any more...
49 * DMA4 is reserved for cascading.
50 */
51
52 struct dma_chan {
53 int lock;
54 const char *device_id;
55 };
56
57 static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = {
58 { 0, 0 },
59 { 0, 0 },
60 { 0, 0 },
61 { 0, 0 },
62 { 1, "cascade" },
63 { 0, 0 },
64 { 0, 0 },
65 { 0, 0 }
66 };
67
68 int get_dma_list(char *buf)
69 {
70 int i, len = 0;
71
72 for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) {
73 if (dma_chan_busy[i].lock) {
74 len += sprintf(buf+len, "%2d: %s\n",
75 i,
76 dma_chan_busy[i].device_id);
77 }
78 }
79 return len;
80 } /* get_dma_list */
81
82
83 int request_dma(unsigned int dmanr, const char * device_id)
84 {
85 if (dmanr >= MAX_DMA_CHANNELS)
86 return -EINVAL;
87
88 if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0)
89 return -EBUSY;
90
91 dma_chan_busy[dmanr].device_id = device_id;
92
93 /* old flag was 0, now contains 1 to indicate busy */
94 return 0;
95 } /* request_dma */
96
97
98 void free_dma(unsigned int dmanr)
99 {
100 if (dmanr >= MAX_DMA_CHANNELS) {
101 printk("Trying to free DMA%d\n", dmanr);
102 return;
103 }
104
105 if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) {
106 printk("Trying to free free DMA%d\n", dmanr);
107 return;
108 }
109
110 } /* free_dma */
111
112 #else
113
114 int request_dma(unsigned int dmanr, const char *device_id)
115 {
116 return -EINVAL;
117 }
118
119 void free_dma(unsigned int dmanr)
120 {
121 }
122
123 int get_dma_list(char *buf)
124 {
125 strcpy(buf, "No DMA\n");
126 return 7;
127 }
128 #endif
129