projects/linux·blob master · refs

149 lines · 3.3 KiB

1// SPDX-License-Identifier: GPL-2.0
2/*
3 * linux/kernel/dma.c: A DMA channel allocator. Inspired by linux/kernel/irq.c.
4 *
5 * Written by Hennus Bergman, 1992.
6 *
7 * 1994/12/26: Changes by Alex Nash to fix a minor bug in /proc/dma.
8 * In the previous version the reported device could end up being wrong,
9 * if a device requested a DMA channel that was already in use.
10 * [It also happened to remove the sizeof(char *) == sizeof(int)
11 * assumption introduced because of those /proc/dma patches. -- Hennus]
12 */
13#include <linux/export.h>
14#include <linux/kernel.h>
15#include <linux/errno.h>
16#include <linux/spinlock.h>
17#include <linux/string.h>
18#include <linux/seq_file.h>
19#include <linux/proc_fs.h>
20#include <linux/init.h>
21#include <asm/dma.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 __init proc_dma_init(void)
139{
140 proc_create_single("dma", 0, NULL, proc_dma_show);
141 return 0;
142}
143
144__initcall(proc_dma_init);
145#endif
146
147EXPORT_SYMBOL(request_dma);
148EXPORT_SYMBOL(free_dma);
149EXPORT_SYMBOL(dma_spin_lock);