1 // SPDX-License-Identifier: GPL-2.0 <<
2 /* 1 /*
3 * linux/kernel/dma.c: A DMA channel allocator 2 * linux/kernel/dma.c: A DMA channel allocator. Inspired by linux/kernel/irq.c.
4 * 3 *
5 * Written by Hennus Bergman, 1992. 4 * Written by Hennus Bergman, 1992.
6 * 5 *
7 * 1994/12/26: Changes by Alex Nash to fix a m 6 * 1994/12/26: Changes by Alex Nash to fix a minor bug in /proc/dma.
8 * In the previous version the reported devi 7 * In the previous version the reported device could end up being wrong,
9 * if a device requested a DMA channel that 8 * if a device requested a DMA channel that was already in use.
10 * [It also happened to remove the sizeof(ch 9 * [It also happened to remove the sizeof(char *) == sizeof(int)
11 * assumption introduced because of those /p 10 * assumption introduced because of those /proc/dma patches. -- Hennus]
12 */ 11 */
13 #include <linux/export.h> 12 #include <linux/export.h>
14 #include <linux/kernel.h> 13 #include <linux/kernel.h>
15 #include <linux/errno.h> 14 #include <linux/errno.h>
16 #include <linux/spinlock.h> 15 #include <linux/spinlock.h>
17 #include <linux/string.h> 16 #include <linux/string.h>
18 #include <linux/seq_file.h> 17 #include <linux/seq_file.h>
19 #include <linux/proc_fs.h> 18 #include <linux/proc_fs.h>
20 #include <linux/init.h> 19 #include <linux/init.h>
21 #include <asm/dma.h> 20 #include <asm/dma.h>
22 21
23 22
24 23
25 /* A note on resource allocation: 24 /* A note on resource allocation:
26 * 25 *
27 * All drivers needing DMA channels, should al 26 * All drivers needing DMA channels, should allocate and release them
28 * through the public routines `request_dma()' 27 * through the public routines `request_dma()' and `free_dma()'.
29 * 28 *
30 * In order to avoid problems, all processes s 29 * In order to avoid problems, all processes should allocate resources in
31 * the same sequence and release them in the r 30 * the same sequence and release them in the reverse order.
32 * 31 *
33 * So, when allocating DMAs and IRQs, first al 32 * So, when allocating DMAs and IRQs, first allocate the IRQ, then the DMA.
34 * When releasing them, first release the DMA, 33 * When releasing them, first release the DMA, then release the IRQ.
35 * If you don't, you may cause allocation requ 34 * If you don't, you may cause allocation requests to fail unnecessarily.
36 * This doesn't really matter now, but it will 35 * This doesn't really matter now, but it will once we get real semaphores
37 * in the kernel. 36 * in the kernel.
38 */ 37 */
39 38
40 39
41 DEFINE_SPINLOCK(dma_spin_lock); 40 DEFINE_SPINLOCK(dma_spin_lock);
42 41
43 /* 42 /*
44 * If our port doesn't define this it has 43 * If our port doesn't define this it has no PC like DMA
45 */ 44 */
46 45
47 #ifdef MAX_DMA_CHANNELS 46 #ifdef MAX_DMA_CHANNELS
48 47
49 48
50 /* Channel n is busy iff dma_chan_busy[n].lock 49 /* Channel n is busy iff dma_chan_busy[n].lock != 0.
51 * DMA0 used to be reserved for DRAM refresh, 50 * DMA0 used to be reserved for DRAM refresh, but apparently not any more...
52 * DMA4 is reserved for cascading. 51 * DMA4 is reserved for cascading.
53 */ 52 */
54 53
55 struct dma_chan { 54 struct dma_chan {
56 int lock; 55 int lock;
57 const char *device_id; 56 const char *device_id;
58 }; 57 };
59 58
60 static struct dma_chan dma_chan_busy[MAX_DMA_C 59 static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = {
61 [4] = { 1, "cascade" }, 60 [4] = { 1, "cascade" },
62 }; 61 };
63 62
64 63
65 /** 64 /**
66 * request_dma - request and reserve a system 65 * request_dma - request and reserve a system DMA channel
67 * @dmanr: DMA channel number 66 * @dmanr: DMA channel number
68 * @device_id: reserving device ID string, use 67 * @device_id: reserving device ID string, used in /proc/dma
69 */ 68 */
70 int request_dma(unsigned int dmanr, const char 69 int request_dma(unsigned int dmanr, const char * device_id)
71 { 70 {
72 if (dmanr >= MAX_DMA_CHANNELS) 71 if (dmanr >= MAX_DMA_CHANNELS)
73 return -EINVAL; 72 return -EINVAL;
74 73
75 if (xchg(&dma_chan_busy[dmanr].lock, 1 74 if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0)
76 return -EBUSY; 75 return -EBUSY;
77 76
78 dma_chan_busy[dmanr].device_id = devic 77 dma_chan_busy[dmanr].device_id = device_id;
79 78
80 /* old flag was 0, now contains 1 to i 79 /* old flag was 0, now contains 1 to indicate busy */
81 return 0; 80 return 0;
82 } /* request_dma */ 81 } /* request_dma */
83 82
84 /** 83 /**
85 * free_dma - free a reserved system DMA chann 84 * free_dma - free a reserved system DMA channel
86 * @dmanr: DMA channel number 85 * @dmanr: DMA channel number
87 */ 86 */
88 void free_dma(unsigned int dmanr) 87 void free_dma(unsigned int dmanr)
89 { 88 {
90 if (dmanr >= MAX_DMA_CHANNELS) { 89 if (dmanr >= MAX_DMA_CHANNELS) {
91 printk(KERN_WARNING "Trying to 90 printk(KERN_WARNING "Trying to free DMA%d\n", dmanr);
92 return; 91 return;
93 } 92 }
94 93
95 if (xchg(&dma_chan_busy[dmanr].lock, 0 94 if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) {
96 printk(KERN_WARNING "Trying to 95 printk(KERN_WARNING "Trying to free free DMA%d\n", dmanr);
97 return; 96 return;
98 } 97 }
99 98
100 } /* free_dma */ 99 } /* free_dma */
101 100
102 #else 101 #else
103 102
104 int request_dma(unsigned int dmanr, const char 103 int request_dma(unsigned int dmanr, const char *device_id)
105 { 104 {
106 return -EINVAL; 105 return -EINVAL;
107 } 106 }
108 107
109 void free_dma(unsigned int dmanr) 108 void free_dma(unsigned int dmanr)
110 { 109 {
111 } 110 }
112 111
113 #endif 112 #endif
114 113
115 #ifdef CONFIG_PROC_FS 114 #ifdef CONFIG_PROC_FS
116 115
117 #ifdef MAX_DMA_CHANNELS 116 #ifdef MAX_DMA_CHANNELS
118 static int proc_dma_show(struct seq_file *m, v 117 static int proc_dma_show(struct seq_file *m, void *v)
119 { 118 {
120 int i; 119 int i;
121 120
122 for (i = 0 ; i < MAX_DMA_CHANNELS ; i+ 121 for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) {
123 if (dma_chan_busy[i].lock) { 122 if (dma_chan_busy[i].lock) {
124 seq_printf(m, "%2d: %s 123 seq_printf(m, "%2d: %s\n", i,
125 dma_chan_bu 124 dma_chan_busy[i].device_id);
126 } 125 }
127 } 126 }
128 return 0; 127 return 0;
129 } 128 }
130 #else 129 #else
131 static int proc_dma_show(struct seq_file *m, v 130 static int proc_dma_show(struct seq_file *m, void *v)
132 { 131 {
133 seq_puts(m, "No DMA\n"); 132 seq_puts(m, "No DMA\n");
134 return 0; 133 return 0;
135 } 134 }
136 #endif /* MAX_DMA_CHANNELS */ 135 #endif /* MAX_DMA_CHANNELS */
137 136
>> 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
138 static int __init proc_dma_init(void) 149 static int __init proc_dma_init(void)
139 { 150 {
140 proc_create_single("dma", 0, NULL, pro !! 151 proc_create("dma", 0, NULL, &proc_dma_operations);
141 return 0; 152 return 0;
142 } 153 }
143 154
144 __initcall(proc_dma_init); 155 __initcall(proc_dma_init);
145 #endif 156 #endif
146 157
147 EXPORT_SYMBOL(request_dma); 158 EXPORT_SYMBOL(request_dma);
148 EXPORT_SYMBOL(free_dma); 159 EXPORT_SYMBOL(free_dma);
149 EXPORT_SYMBOL(dma_spin_lock); 160 EXPORT_SYMBOL(dma_spin_lock);
150 161
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