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
  41 spinlock_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
  55 struct dma_chan {
  56         int  lock;
  57         const char *device_id;
  58 };
  59
  60 static 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
  72 int 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
  87 void 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 static 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
 116 int request_dma(unsigned int dmanr, const char *device_id)
 117 {
 118         return -EINVAL;
 119 }
 120
 121 void free_dma(unsigned int dmanr)
 122 {
 123 }
 124
 125 static 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
 134 static 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
 152 static 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
 159 static 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
 173 EXPORT_SYMBOL(request_dma);
 174 EXPORT_SYMBOL(free_dma);
 175 EXPORT_SYMBOL(dma_spin_lock);