kernel/dma.c

/* */
This source file includes following definitions.
get_dma_list
request_dma
free_dma
   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 
  41 struct dma_chan {
  42         int  lock;
  43         const char *device_id;
  44 };
  45 
  46 static 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 
  57 int 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 
  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("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 */
/* */
root/kernel/dma.c

DEFINITIONS
