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);