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- /* $Id: dma.c,v 1.1.1.1 2007/06/12 07:27:11 eyryu 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/module.h>
- #include <linux/kernel.h>
- #include <linux/errno.h>
- #include <linux/spinlock.h>
- #include <linux/string.h>
- #include <linux/seq_file.h>
- #include <linux/proc_fs.h>
- #include <linux/init.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.
- */
- 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)
- {
- struct proc_dir_entry *e;
- e = create_proc_entry("dma", 0, NULL);
- if (e)
- e->proc_fops = &proc_dma_operations;
- return 0;
- }
- __initcall(proc_dma_init);
- #endif
- EXPORT_SYMBOL(request_dma);
- EXPORT_SYMBOL(free_dma);
- EXPORT_SYMBOL(dma_spin_lock);
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