LXR linux-old/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
  38spinlock_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
  52struct dma_chan {
  53        int  lock;
  54        const char *device_id;
  55};
  56
  57static 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
  68int 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
  83int 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
  98void 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
 114int request_dma(unsigned int dmanr, const char *device_id)
 115{
 116        return -EINVAL;
 117}
 118
 119void free_dma(unsigned int dmanr)
 120{
 121}
 122
 123int get_dma_list(char *buf)
 124{       
 125        strcpy(buf, "No DMA\n");
 126        return 7;
 127}
 128#endif
 129