kernel/dma.c

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 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 <linux/spinlock.h>
 16 #include <asm/dma.h>
 17 #include <asm/system.h>
 18
 19
 20 /* A note on resource allocation:
 21  *
 22  * All drivers needing DMA channels, should allocate and release them
 23  * through the public routines `request_dma()' and `free_dma()'.
 24  *
 25  * In order to avoid problems, all processes should allocate resources in
 26  * the same sequence and release them in the reverse order.
 27  *
 28  * So, when allocating DMAs and IRQs, first allocate the IRQ, then the DMA.
 29  * When releasing them, first release the DMA, then release the IRQ.
 30  * If you don't, you may cause allocation requests to fail unnecessarily.
 31  * This doesn't really matter now, but it will once we get real semaphores
 32  * in the kernel.
 33  */
 34
 35
 36 spinlock_t dma_spin_lock = SPIN_LOCK_UNLOCKED;
 37
 38
 39 /* Channel n is busy iff dma_chan_busy[n].lock != 0.
 40  * DMA0 used to be reserved for DRAM refresh, but apparently not any more...
 41  * DMA4 is reserved for cascading.
 42  */
 43
 44 struct dma_chan {
 45 int lock;
 46 const char*device_id;
 47 };
 48
 49 static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = {
 50 {0,0},
 51 {0,0},
 52 {0,0},
 53 {0,0},
 54 {1,"cascade"},
 55 {0,0},
 56 {0,0},
 57 {0,0}
 58 };
 59
 60 intget_dma_list(char*buf)
 61 {
 62 int i, len =0;
 63
 64 for(i =0; i < MAX_DMA_CHANNELS ; i++) {
 65 if(dma_chan_busy[i].lock) {
 66  len +=sprintf(buf+len,"%2d: %s\n",
 67  i,
 68  dma_chan_busy[i].device_id);
 69 }
 70 }
 71 return len;
 72 }/* get_dma_list */
 73
 74
 75 intrequest_dma(unsigned int dmanr,const char* device_id)
 76 {
 77 if(dmanr >= MAX_DMA_CHANNELS)
 78 return-EINVAL;
 79
 80 if(xchg(&dma_chan_busy[dmanr].lock,1) !=0)
 81 return-EBUSY;
 82
 83  dma_chan_busy[dmanr].device_id = device_id;
 84
 85 /* old flag was 0, now contains 1 to indicate busy */
 86 return0;
 87 }/* request_dma */
 88
 89
 90 voidfree_dma(unsigned int dmanr)
 91 {
 92 if(dmanr >= MAX_DMA_CHANNELS) {
 93 printk("Trying to free DMA%d\n", dmanr);
 94 return;
 95 }
 96
 97 if(xchg(&dma_chan_busy[dmanr].lock,0) ==0) {
 98 printk("Trying to free free DMA%d\n", dmanr);
 99 return;
 100 }
 101
 102 }/* free_dma */