LXR RHEL4/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
  41spinlock_t dma_spin_lock = SPIN_LOCK_UNLOCKED;
  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
  55struct dma_chan {
  56        int  lock;
  57        const char *device_id;
  58};
  59
  60static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = {
  61        [4] = { 1, "cascade" },
  62};
  63
  64
  65int 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
  80void 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
  96int request_dma(unsigned int dmanr, const char *device_id)
  97{
  98        return -EINVAL;
  99}
 100
 101void free_dma(unsigned int dmanr)
 102{
 103}
 104
 105#endif
 106
 107#ifdef CONFIG_PROC_FS
 108
 109#ifdef MAX_DMA_CHANNELS
 110static 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
 123static 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
 130static int proc_dma_open(struct inode *inode, struct file *file)
 131{
 132        return single_open(file, proc_dma_show, NULL);
 133}
 134
 135static 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
 142static 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
 156EXPORT_SYMBOL(request_dma);
 157EXPORT_SYMBOL(free_dma);
 158EXPORT_SYMBOL(dma_spin_lock);
 159