/* * 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 #include #include #include #include #include #include #include #include /* 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. */ DEFINE_SPINLOCK(dma_spin_lock); /* * 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] = { [4] = { 1, "cascade" }, }; /** * request_dma - request and reserve a system DMA channel * @dmanr: DMA channel number * @device_id: reserving device ID string, used in /proc/dma */ 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 */ /** * free_dma - free a reserved system DMA channel * @dmanr: DMA channel number */ void free_dma(unsigned int dmanr) { if (dmanr >= MAX_DMA_CHANNELS) { printk(KERN_WARNING "Trying to free DMA%d\n", dmanr); return; } if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) { printk(KERN_WARNING "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) { } #endif #ifdef CONFIG_PROC_FS #ifdef MAX_DMA_CHANNELS static int proc_dma_show(struct seq_file *m, void *v) { int i; for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) { if (dma_chan_busy[i].lock) { seq_printf(m, "%2d: %s\n", i, dma_chan_busy[i].device_id); } } return 0; } #else static int proc_dma_show(struct seq_file *m, void *v) { seq_puts(m, "No DMA\n"); return 0; } #endif /* MAX_DMA_CHANNELS */ static int proc_dma_open(struct inode *inode, struct file *file) { return single_open(file, proc_dma_show, NULL); } static const struct file_operations proc_dma_operations = { .open = proc_dma_open, .read = seq_read, .llseek = seq_lseek, .release = single_release, }; static int __init proc_dma_init(void) { proc_create("dma", 0, NULL, &proc_dma_operations); return 0; } __initcall(proc_dma_init); #endif EXPORT_SYMBOL(request_dma); EXPORT_SYMBOL(free_dma); EXPORT_SYMBOL(dma_spin_lock); >)AuthorFilesLines