kernel/dma.c

   1 /* $Id: dma.c,v 1.7 1994/12/28 03:35:33 root Exp root $
   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/module.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 #include <asm/system.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 int request_dma(unsigned int dmanr, const char * device_id)
  66 {
  67         if (dmanr >= MAX_DMA_CHANNELS)
  68                 return -EINVAL;
  69
  70         if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0)
  71                 return -EBUSY;
  72
  73         dma_chan_busy[dmanr].device_id = device_id;
  74
  75         /* old flag was 0, now contains 1 to indicate busy */
  76         return 0;
  77 } /* request_dma */
  78
  79
  80 void free_dma(unsigned int dmanr)
  81 {
  82         if (dmanr >= MAX_DMA_CHANNELS) {
  83                 printk(KERN_WARNING "Trying to free DMA%d\n", dmanr);
  84                 return;
  85         }
  86
  87         if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) {
  88                 printk(KERN_WARNING "Trying to free free DMA%d\n", dmanr);
  89                 return;
  90         }
  91
  92 } /* free_dma */
  93
  94 #else
  95
  96 int request_dma(unsigned int dmanr, const char *device_id)
  97 {
  98         return -EINVAL;
  99 }
 100
 101 void free_dma(unsigned int dmanr)
 102 {
 103 }
 104
 105 #endif
 106
 107 #ifdef CONFIG_PROC_FS
 108
 109 #ifdef MAX_DMA_CHANNELS
 110 static int proc_dma_show(struct seq_file *m, void *v)
 111 {
 112         int i;
 113
 114         for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) {
 115                 if (dma_chan_busy[i].lock) {
 116                     seq_printf(m, "%2d: %s\n", i,
 117                                dma_chan_busy[i].device_id);
 118                 }
 119         }
 120         return 0;
 121 }
 122 #else
 123 static int proc_dma_show(struct seq_file *m, void *v)
 124 {
 125         seq_puts(m, "No DMA\n");
 126         return 0;
 127 }
 128 #endif /* MAX_DMA_CHANNELS */
 129
 130 static int proc_dma_open(struct inode *inode, struct file *file)
 131 {
 132         return single_open(file, proc_dma_show, NULL);
 133 }
 134
 135 static struct file_operations proc_dma_operations = {
 136         .open           = proc_dma_open,
 137         .read           = seq_read,
 138         .llseek         = seq_lseek,
 139         .release        = single_release,
 140 };
 141
 142 static int __init proc_dma_init(void)
 143 {
 144         struct proc_dir_entry *e;
 145
 146         e = create_proc_entry("dma", 0, NULL);
 147         if (e)
 148                 e->proc_fops = &proc_dma_operations;
 149
 150         return 0;
 151 }
 152
 153 __initcall(proc_dma_init);
 154 #endif
 155
 156 EXPORT_SYMBOL(request_dma);
 157 EXPORT_SYMBOL(free_dma);
 158 EXPORT_SYMBOL(dma_spin_lock);