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.
4 * Written by Hennus Bergman, 1992.
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]
13 #include <linux/kernel.h>
14 #include <linux/errno.h>
15 #include <linux/spinlock.h>
16 #include <linux/string.h>
18 #include <asm/system.h>
22 /* A note on resource allocation:
24 * All drivers needing DMA channels, should allocate and release them
25 * through the public routines `request_dma()' and `free_dma()'.
27 * In order to avoid problems, all processes should allocate resources in
28 * the same sequence and release them in the reverse order.
30 * So, when allocating DMAs and IRQs, first allocate the IRQ, then the DMA.
31 * When releasing them, first release the DMA, then release the IRQ.
32 * If you don't, you may cause allocation requests to fail unnecessarily.
33 * This doesn't really matter now, but it will once we get real semaphores
38 spinlock_t dma_spin_lock = SPIN_LOCK_UNLOCKED;
41 * If our port doesn't define this it has no PC like DMA
44 #ifdef MAX_DMA_CHANNELS
47 /* Channel n is busy iff dma_chan_busy[n].lock != 0.
48 * DMA0 used to be reserved for DRAM refresh, but apparently not any more...
49 * DMA4 is reserved for cascading.
54 const char *device_id;
57 static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = {
68 int get_dma_list(char *buf)
72 for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) {
73 if (dma_chan_busy[i].lock) {
74 len += sprintf(buf+len, "%2d: %s\n",
76 dma_chan_busy[i].device_id);
83 int request_dma(unsigned int dmanr, const char * device_id)
85 if (dmanr >= MAX_DMA_CHANNELS)
88 if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0)
91 dma_chan_busy[dmanr].device_id = device_id;
93 /* old flag was 0, now contains 1 to indicate busy */
98 void free_dma(unsigned int dmanr)
100 if (dmanr >= MAX_DMA_CHANNELS) {
101 printk("Trying to free DMA%d\n", dmanr);
105 if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) {
106 printk("Trying to free free DMA%d\n", dmanr);
114 int request_dma(unsigned int dmanr, const char *device_id)
119 void free_dma(unsigned int dmanr)
123 int get_dma_list(char *buf)
125 strcpy(buf, "No DMA\n");