LXR linux-bk/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        { 0, 0 },
  62        { 0, 0 },
  63        { 0, 0 },
  64        { 0, 0 },
  65        { 1, "cascade" },
  66        { 0, 0 },
  67        { 0, 0 },
  68        { 0, 0 }
  69};
  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(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
 101static int proc_dma_show(struct seq_file *m, void *v)
 102{
 103        int i;
 104
 105        for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) {
 106                if (dma_chan_busy[i].lock) {
 107                    seq_printf(m, "%2d: %s\n", i,
 108                               dma_chan_busy[i].device_id);
 109                }
 110        }
 111        return 0;
 112}
 113
 114#else
 115
 116int request_dma(unsigned int dmanr, const char *device_id)
 117{
 118        return -EINVAL;
 119}
 120
 121void free_dma(unsigned int dmanr)
 122{
 123}
 124
 125static int proc_dma_show(struct seq_file *m, void *v)
 126{
 127        seq_puts(m, "No DMA\n");
 128        return 0;
 129}
 130
 131#endif
 132
 133#ifdef CONFIG_PROC_FS
 134static int proc_dma_open(struct inode *inode, struct file *file)
 135{
 136        char *buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
 137        struct seq_file *m;
 138        int res;
 139
 140        if (!buf)
 141                return -ENOMEM;
 142        res = single_open(file, proc_dma_show, NULL);
 143        if (!res) {
 144                m = file->private_data;
 145                m->buf = buf;
 146                m->size = PAGE_SIZE;
 147        } else
 148                kfree(buf);
 149        return res;
 150}
 151
 152static struct file_operations proc_dma_operations = {
 153        .open           = proc_dma_open,
 154        .read           = seq_read,
 155        .llseek         = seq_lseek,
 156        .release        = single_release,
 157};
 158
 159static int __init proc_dma_init(void)
 160{
 161        struct proc_dir_entry *e;
 162
 163        e = create_proc_entry("dma", 0, NULL);
 164        if (e)
 165                e->proc_fops = &proc_dma_operations;
 166
 167        return 0;
 168}
 169
 170__initcall(proc_dma_init);
 171#endif
 172
 173EXPORT_SYMBOL(request_dma);
 174EXPORT_SYMBOL(free_dma);
 175EXPORT_SYMBOL(dma_spin_lock);
 176