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 
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  */
request_dma(unsigned int dmanr,const char * device_id)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  */
free_dma(unsigned int dmanr)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 
request_dma(unsigned int dmanr,const char * device_id)104 int request_dma(unsigned int dmanr, const char *device_id)
105 {
106 	return -EINVAL;
107 }
108 
free_dma(unsigned int dmanr)109 void free_dma(unsigned int dmanr)
110 {
111 }
112 
113 #endif
114 
115 #ifdef CONFIG_PROC_FS
116 
117 #ifdef MAX_DMA_CHANNELS
proc_dma_show(struct seq_file * m,void * v)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
proc_dma_show(struct seq_file * m,void * v)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 
proc_dma_init(void)138 static 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 
147 EXPORT_SYMBOL(request_dma);
148 EXPORT_SYMBOL(free_dma);
149 EXPORT_SYMBOL(dma_spin_lock);
150