LXR linux/kernel/dma.c

   1/*
   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/export.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
  22
  23
  24/* A note on resource allocation:
  25 *
  26 * All drivers needing DMA channels, should allocate and release them
  27 * through the public routines `request_dma()' and `free_dma()'.
  28 *
  29 * In order to avoid problems, all processes should allocate resources in
  30 * the same sequence and release them in the reverse order.
  31 *
  32 * So, when allocating DMAs and IRQs, first allocate the IRQ, then the DMA.
  33 * When releasing them, first release the DMA, then release the IRQ.
  34 * If you don't, you may cause allocation requests to fail unnecessarily.
  35 * This doesn't really matter now, but it will once we get real semaphores
  36 * in the kernel.
  37 */
  38
  39
  40DEFINE_SPINLOCK(dma_spin_lock);
  41
  42/*
  43 *      If our port doesn't define this it has no PC like DMA
  44 */
  45
  46#ifdef MAX_DMA_CHANNELS
  47
  48
  49/* Channel n is busy iff dma_chan_busy[n].lock != 0.
  50 * DMA0 used to be reserved for DRAM refresh, but apparently not any more...
  51 * DMA4 is reserved for cascading.
  52 */
  53
  54struct dma_chan {
  55        int  lock;
  56        const char *device_id;
  57};
  58
  59static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = {
  60        [4] = { 1, "cascade" },
  61};
  62
  63
  64/**
  65 * request_dma - request and reserve a system DMA channel
  66 * @dmanr: DMA channel number
  67 * @device_id: reserving device ID string, used in /proc/dma
  68 */
  69int request_dma(unsigned int dmanr, const char * device_id)
  70{
  71        if (dmanr >= MAX_DMA_CHANNELS)
  72                return -EINVAL;
  73
  74        if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0)
  75                return -EBUSY;
  76
  77        dma_chan_busy[dmanr].device_id = device_id;
  78
  79        /* old flag was 0, now contains 1 to indicate busy */
  80        return 0;
  81} /* request_dma */
  82
  83/**
  84 * free_dma - free a reserved system DMA channel
  85 * @dmanr: DMA channel number
  86 */
  87void free_dma(unsigned int dmanr)
  88{
  89        if (dmanr >= MAX_DMA_CHANNELS) {
  90                printk(KERN_WARNING "Trying to free DMA%d\n", dmanr);
  91                return;
  92        }
  93
  94        if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) {
  95                printk(KERN_WARNING "Trying to free free DMA%d\n", dmanr);
  96                return;
  97        }
  98
  99} /* free_dma */
 100
 101#else
 102
 103int request_dma(unsigned int dmanr, const char *device_id)
 104{
 105        return -EINVAL;
 106}
 107
 108void free_dma(unsigned int dmanr)
 109{
 110}
 111
 112#endif
 113
 114#ifdef CONFIG_PROC_FS
 115
 116#ifdef MAX_DMA_CHANNELS
 117static int proc_dma_show(struct seq_file *m, void *v)
 118{
 119        int i;
 120
 121        for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) {
 122                if (dma_chan_busy[i].lock) {
 123                        seq_printf(m, "%2d: %s\n", i,
 124                                   dma_chan_busy[i].device_id);
 125                }
 126        }
 127        return 0;
 128}
 129#else
 130static int proc_dma_show(struct seq_file *m, void *v)
 131{
 132        seq_puts(m, "No DMA\n");
 133        return 0;
 134}
 135#endif /* MAX_DMA_CHANNELS */
 136
 137static int proc_dma_open(struct inode *inode, struct file *file)
 138{
 139        return single_open(file, proc_dma_show, NULL);
 140}
 141
 142static const struct file_operations proc_dma_operations = {
 143        .open           = proc_dma_open,
 144        .read           = seq_read,
 145        .llseek         = seq_lseek,
 146        .release        = single_release,
 147};
 148
 149static int __init proc_dma_init(void)
 150{
 151        proc_create("dma", 0, NULL, &proc_dma_operations);
 152        return 0;
 153}
 154
 155__initcall(proc_dma_init);
 156#endif
 157
 158EXPORT_SYMBOL(request_dma);
 159EXPORT_SYMBOL(free_dma);
 160EXPORT_SYMBOL(dma_spin_lock);
 161