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 <asm/dma.h>
  16#include <asm/system.h>
  17
  18
  19/* A note on resource allocation:
  20 *
  21 * All drivers needing DMA channels, should allocate and release them
  22 * through the public routines `request_dma()' and `free_dma()'.
  23 *
  24 * In order to avoid problems, all processes should allocate resources in
  25 * the same sequence and release them in the reverse order.
  26 *
  27 * So, when allocating DMAs and IRQs, first allocate the IRQ, then the DMA.
  28 * When releasing them, first release the DMA, then release the IRQ.
  29 * If you don't, you may cause allocation requests to fail unnecessarily.
  30 * This doesn't really matter now, but it will once we get real semaphores
  31 * in the kernel.
  32 */
  33
  34
  35
  36/* Channel n is busy iff dma_chan_busy[n].lock != 0.
  37 * DMA0 used to be reserved for DRAM refresh, but apparently not any more...
  38 * DMA4 is reserved for cascading.
  39 */
  40
  41struct dma_chan {
  42        int  lock;
  43        const char *device_id;
  44};
  45
  46static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = {
  47        { 0, 0 },
  48        { 0, 0 },
  49        { 0, 0 },
  50        { 0, 0 },
  51        { 1, "cascade" },
  52        { 0, 0 },
  53        { 0, 0 },
  54        { 0, 0 }
  55};
  56
  57int get_dma_list(char *buf)
  58{
  59        int i, len = 0;
  60
  61        for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) {
  62                if (dma_chan_busy[i].lock) {
  63                    len += sprintf(buf+len, "%2d: %s\n",
  64                                   i,
  65                                   dma_chan_busy[i].device_id);
  66                }
  67        }
  68        return len;
  69} /* get_dma_list */
  70
  71
  72int request_dma(unsigned int dmanr, const char * device_id)
  73{
  74        if (dmanr >= MAX_DMA_CHANNELS)
  75                return -EINVAL;
  76
  77        if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0)
  78                return -EBUSY;
  79
  80        dma_chan_busy[dmanr].device_id = device_id;
  81
  82        /* old flag was 0, now contains 1 to indicate busy */
  83        return 0;
  84} /* request_dma */
  85
  86
  87void free_dma(unsigned int dmanr)
  88{
  89        if (dmanr >= MAX_DMA_CHANNELS) {
  90                printk("Trying to free DMA%d\n", dmanr);
  91                return;
  92        }
  93
  94        if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) {
  95                printk("Trying to free free DMA%d\n", dmanr);
  96                return;
  97        }       
  98
  99} /* free_dma */
 100