| /* $Id: dma.c,v 1.7 1994/12/28 03:35:33 root Exp root $ |
| * linux/kernel/dma.c: A DMA channel allocator. Inspired by linux/kernel/irq.c. |
| * |
| * Written by Hennus Bergman, 1992. |
| * |
| * 1994/12/26: Changes by Alex Nash to fix a minor bug in /proc/dma. |
| * In the previous version the reported device could end up being wrong, |
| * if a device requested a DMA channel that was already in use. |
| * [It also happened to remove the sizeof(char *) == sizeof(int) |
| * assumption introduced because of those /proc/dma patches. -- Hennus] |
| */ |
| |
| #include <linux/kernel.h> |
| #include <linux/errno.h> |
| #include <linux/spinlock.h> |
| #include <linux/string.h> |
| #include <asm/dma.h> |
| #include <asm/system.h> |
| |
| |
| |
| /* A note on resource allocation: |
| * |
| * All drivers needing DMA channels, should allocate and release them |
| * through the public routines `request_dma()' and `free_dma()'. |
| * |
| * In order to avoid problems, all processes should allocate resources in |
| * the same sequence and release them in the reverse order. |
| * |
| * So, when allocating DMAs and IRQs, first allocate the IRQ, then the DMA. |
| * When releasing them, first release the DMA, then release the IRQ. |
| * If you don't, you may cause allocation requests to fail unnecessarily. |
| * This doesn't really matter now, but it will once we get real semaphores |
| * in the kernel. |
| */ |
| |
| |
| spinlock_t dma_spin_lock = SPIN_LOCK_UNLOCKED; |
| |
| /* |
| * If our port doesn't define this it has no PC like DMA |
| */ |
| |
| #ifdef MAX_DMA_CHANNELS |
| |
| |
| /* Channel n is busy iff dma_chan_busy[n].lock != 0. |
| * DMA0 used to be reserved for DRAM refresh, but apparently not any more... |
| * DMA4 is reserved for cascading. |
| */ |
| |
| struct dma_chan { |
| int lock; |
| const char *device_id; |
| }; |
| |
| static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = { |
| { 0, 0 }, |
| { 0, 0 }, |
| { 0, 0 }, |
| { 0, 0 }, |
| { 1, "cascade" }, |
| { 0, 0 }, |
| { 0, 0 }, |
| { 0, 0 } |
| }; |
| |
| int get_dma_list(char *buf) |
| { |
| int i, len = 0; |
| |
| for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) { |
| if (dma_chan_busy[i].lock) { |
| len += sprintf(buf+len, "%2d: %s\n", |
| i, |
| dma_chan_busy[i].device_id); |
| } |
| } |
| return len; |
| } /* get_dma_list */ |
| |
| |
| int request_dma(unsigned int dmanr, const char * device_id) |
| { |
| if (dmanr >= MAX_DMA_CHANNELS) |
| return -EINVAL; |
| |
| if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0) |
| return -EBUSY; |
| |
| dma_chan_busy[dmanr].device_id = device_id; |
| |
| /* old flag was 0, now contains 1 to indicate busy */ |
| return 0; |
| } /* request_dma */ |
| |
| |
| void free_dma(unsigned int dmanr) |
| { |
| if (dmanr >= MAX_DMA_CHANNELS) { |
| printk("Trying to free DMA%d\n", dmanr); |
| return; |
| } |
| |
| if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) { |
| printk("Trying to free free DMA%d\n", dmanr); |
| return; |
| } |
| |
| } /* free_dma */ |
| |
| #else |
| |
| int request_dma(unsigned int dmanr, const char *device_id) |
| { |
| return -EINVAL; |
| } |
| |
| void free_dma(unsigned int dmanr) |
| { |
| } |
| |
| int get_dma_list(char *buf) |
| { |
| strcpy(buf, "No DMA\n"); |
| return 7; |
| } |
| #endif |