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
  13 #include <linux/kernel.h>
  14 #include <linux/errno.h>
  15 #include <linux/spinlock.h>
  16 #include <asm/dma.h>
  17 #include <asm/system.h>
  18
  19
  20
  21 /* A note on resource allocation:
  22  *
  23  * All drivers needing DMA channels, should allocate and release them
  24  * through the public routines `request_dma()' and `free_dma()'.
  25  *
  26  * In order to avoid problems, all processes should allocate resources in
  27  * the same sequence and release them in the reverse order.
  28  *
  29  * So, when allocating DMAs and IRQs, first allocate the IRQ, then the DMA.
  30  * When releasing them, first release the DMA, then release the IRQ.
  31  * If you don't, you may cause allocation requests to fail unnecessarily.
  32  * This doesn't really matter now, but it will once we get real semaphores
  33  * in the kernel.
  34  */
  35
  36
  37 spinlock_t dma_spin_lock = SPIN_LOCK_UNLOCKED;
  38
  39 /*
  40  *      If our port doesn't define this it has no PC like DMA
  41  */
  42
  43 #ifdef MAX_DMA_CHANNELS
  44
  45
  46 /* Channel n is busy iff dma_chan_busy[n].lock != 0.
  47  * DMA0 used to be reserved for DRAM refresh, but apparently not any more...
  48  * DMA4 is reserved for cascading.
  49  */
  50
  51 struct dma_chan {
  52         int  lock;
  53         const char *device_id;
  54 };
  55
  56 static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = {
  57         { 0, 0 },
  58         { 0, 0 },
  59         { 0, 0 },
  60         { 0, 0 },
  61         { 1, "cascade" },
  62         { 0, 0 },
  63         { 0, 0 },
  64         { 0, 0 }
  65 };
  66
  67 int get_dma_list(char *buf)
  68 {
  69         int i, len = 0;
  70
  71         for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) {
  72                 if (dma_chan_busy[i].lock) {
  73                     len += sprintf(buf+len, "%2d: %s\n",
  74                                    i,
  75                                    dma_chan_busy[i].device_id);
  76                 }
  77         }
  78         return len;
  79 } /* get_dma_list */
  80
  81
  82 int request_dma(unsigned int dmanr, const char * device_id)
  83 {
  84         if (dmanr >= MAX_DMA_CHANNELS)
  85                 return -EINVAL;
  86
  87         if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0)
  88                 return -EBUSY;
  89
  90         dma_chan_busy[dmanr].device_id = device_id;
  91
  92         /* old flag was 0, now contains 1 to indicate busy */
  93         return 0;
  94 } /* request_dma */
  95
  96
  97 void free_dma(unsigned int dmanr)
  98 {
  99         if (dmanr >= MAX_DMA_CHANNELS) {
 100                 printk("Trying to free DMA%d\n", dmanr);
 101                 return;
 102         }
 103
 104         if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) {
 105                 printk("Trying to free free DMA%d\n", dmanr);
 106                 return;
 107         }
 108
 109 } /* free_dma */
 110
 111 #else
 112
 113 int request_dma(unsigned int dmanr, const char *device_id)
 114 {
 115         return -EINVAL;
 116 }
 117
 118 int free_dma(unsigned int dmanr)
 119 {
 120         return -EINVAL;
 121 }
 122
 123 int get_dma_list(char *buf)
 124 {
 125         strcpy(buf, "No DMA\n");
 126         return 7;
 127 }
 128 #endif