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Linux/kernel/dma.c

  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/export.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 
 22 
 23 
 24 /* A note on resource allocation:
 25  *
 26  * All drivers needing DMA channels, should allocate and release them
 27  * through the public routines `request_dma()' and `free_dma()'.
 28  *
 29  * In order to avoid problems, all processes should allocate resources in
 30  * the same sequence and release them in the reverse order.
 31  *
 32  * So, when allocating DMAs and IRQs, first allocate the IRQ, then the DMA.
 33  * When releasing them, first release the DMA, then release the IRQ.
 34  * If you don't, you may cause allocation requests to fail unnecessarily.
 35  * This doesn't really matter now, but it will once we get real semaphores
 36  * in the kernel.
 37  */
 38 
 39 
 40 DEFINE_SPINLOCK(dma_spin_lock);
 41 
 42 /*
 43  *      If our port doesn't define this it has no PC like DMA
 44  */
 45 
 46 #ifdef MAX_DMA_CHANNELS
 47 
 48 
 49 /* Channel n is busy iff dma_chan_busy[n].lock != 0.
 50  * DMA0 used to be reserved for DRAM refresh, but apparently not any more...
 51  * DMA4 is reserved for cascading.
 52  */
 53 
 54 struct dma_chan {
 55         int  lock;
 56         const char *device_id;
 57 };
 58 
 59 static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = {
 60         [4] = { 1, "cascade" },
 61 };
 62 
 63 
 64 /**
 65  * request_dma - request and reserve a system DMA channel
 66  * @dmanr: DMA channel number
 67  * @device_id: reserving device ID string, used in /proc/dma
 68  */
 69 int request_dma(unsigned int dmanr, const char * device_id)
 70 {
 71         if (dmanr >= MAX_DMA_CHANNELS)
 72                 return -EINVAL;
 73 
 74         if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0)
 75                 return -EBUSY;
 76 
 77         dma_chan_busy[dmanr].device_id = device_id;
 78 
 79         /* old flag was 0, now contains 1 to indicate busy */
 80         return 0;
 81 } /* request_dma */
 82 
 83 /**
 84  * free_dma - free a reserved system DMA channel
 85  * @dmanr: DMA channel number
 86  */
 87 void free_dma(unsigned int dmanr)
 88 {
 89         if (dmanr >= MAX_DMA_CHANNELS) {
 90                 printk(KERN_WARNING "Trying to free DMA%d\n", dmanr);
 91                 return;
 92         }
 93 
 94         if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) {
 95                 printk(KERN_WARNING "Trying to free free DMA%d\n", dmanr);
 96                 return;
 97         }
 98 
 99 } /* free_dma */
100 
101 #else
102 
103 int request_dma(unsigned int dmanr, const char *device_id)
104 {
105         return -EINVAL;
106 }
107 
108 void free_dma(unsigned int dmanr)
109 {
110 }
111 
112 #endif
113 
114 #ifdef CONFIG_PROC_FS
115 
116 #ifdef MAX_DMA_CHANNELS
117 static int proc_dma_show(struct seq_file *m, void *v)
118 {
119         int i;
120 
121         for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) {
122                 if (dma_chan_busy[i].lock) {
123                         seq_printf(m, "%2d: %s\n", i,
124                                    dma_chan_busy[i].device_id);
125                 }
126         }
127         return 0;
128 }
129 #else
130 static int proc_dma_show(struct seq_file *m, void *v)
131 {
132         seq_puts(m, "No DMA\n");
133         return 0;
134 }
135 #endif /* MAX_DMA_CHANNELS */
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 
149 static int __init proc_dma_init(void)
150 {
151         proc_create("dma", 0, NULL, &proc_dma_operations);
152         return 0;
153 }
154 
155 __initcall(proc_dma_init);
156 #endif
157 
158 EXPORT_SYMBOL(request_dma);
159 EXPORT_SYMBOL(free_dma);
160 EXPORT_SYMBOL(dma_spin_lock);
161 

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