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