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[/] [or1k/] [trunk/] [linux/] [linux-2.4/] [kernel/] [dma.c] - Rev 1774
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/* $Id: dma.c,v 1.1.1.1 2004-04-15 02:30:21 phoenix Exp $ * 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
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