Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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. |
| 3 | * |
| 4 | * Written by Hennus Bergman, 1992. |
| 5 | * |
| 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] |
| 11 | */ |
| 12 | #include <linux/module.h> |
| 13 | #include <linux/kernel.h> |
| 14 | #include <linux/errno.h> |
| 15 | #include <linux/spinlock.h> |
| 16 | #include <linux/string.h> |
| 17 | #include <linux/seq_file.h> |
| 18 | #include <linux/proc_fs.h> |
| 19 | #include <linux/init.h> |
| 20 | #include <asm/dma.h> |
| 21 | #include <asm/system.h> |
| 22 | |
| 23 | |
| 24 | |
| 25 | /* A note on resource allocation: |
| 26 | * |
| 27 | * All drivers needing DMA channels, should allocate and release them |
| 28 | * through the public routines `request_dma()' and `free_dma()'. |
| 29 | * |
| 30 | * In order to avoid problems, all processes should allocate resources in |
| 31 | * the same sequence and release them in the reverse order. |
| 32 | * |
| 33 | * So, when allocating DMAs and IRQs, first allocate the IRQ, then the DMA. |
| 34 | * When releasing them, first release the DMA, then release the IRQ. |
| 35 | * If you don't, you may cause allocation requests to fail unnecessarily. |
| 36 | * This doesn't really matter now, but it will once we get real semaphores |
| 37 | * in the kernel. |
| 38 | */ |
| 39 | |
| 40 | |
| 41 | DEFINE_SPINLOCK(dma_spin_lock); |
| 42 | |
| 43 | /* |
| 44 | * If our port doesn't define this it has no PC like DMA |
| 45 | */ |
| 46 | |
| 47 | #ifdef MAX_DMA_CHANNELS |
| 48 | |
| 49 | |
| 50 | /* Channel n is busy iff dma_chan_busy[n].lock != 0. |
| 51 | * DMA0 used to be reserved for DRAM refresh, but apparently not any more... |
| 52 | * DMA4 is reserved for cascading. |
| 53 | */ |
| 54 | |
| 55 | struct dma_chan { |
| 56 | int lock; |
| 57 | const char *device_id; |
| 58 | }; |
| 59 | |
| 60 | static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = { |
| 61 | [4] = { 1, "cascade" }, |
| 62 | }; |
| 63 | |
| 64 | |
Randy Dunlap | eed34d0 | 2006-10-03 01:13:50 -0700 | [diff] [blame] | 65 | /** |
| 66 | * request_dma - request and reserve a system DMA channel |
| 67 | * @dmanr: DMA channel number |
| 68 | * @device_id: reserving device ID string, used in /proc/dma |
| 69 | */ |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 70 | int request_dma(unsigned int dmanr, const char * device_id) |
| 71 | { |
| 72 | if (dmanr >= MAX_DMA_CHANNELS) |
| 73 | return -EINVAL; |
| 74 | |
| 75 | if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0) |
| 76 | return -EBUSY; |
| 77 | |
| 78 | dma_chan_busy[dmanr].device_id = device_id; |
| 79 | |
| 80 | /* old flag was 0, now contains 1 to indicate busy */ |
| 81 | return 0; |
| 82 | } /* request_dma */ |
| 83 | |
Randy Dunlap | eed34d0 | 2006-10-03 01:13:50 -0700 | [diff] [blame] | 84 | /** |
| 85 | * free_dma - free a reserved system DMA channel |
| 86 | * @dmanr: DMA channel number |
| 87 | */ |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 88 | void free_dma(unsigned int dmanr) |
| 89 | { |
| 90 | if (dmanr >= MAX_DMA_CHANNELS) { |
| 91 | printk(KERN_WARNING "Trying to free DMA%d\n", dmanr); |
| 92 | return; |
| 93 | } |
| 94 | |
| 95 | if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) { |
| 96 | printk(KERN_WARNING "Trying to free free DMA%d\n", dmanr); |
| 97 | return; |
| 98 | } |
| 99 | |
| 100 | } /* free_dma */ |
| 101 | |
| 102 | #else |
| 103 | |
| 104 | int request_dma(unsigned int dmanr, const char *device_id) |
| 105 | { |
| 106 | return -EINVAL; |
| 107 | } |
| 108 | |
| 109 | void free_dma(unsigned int dmanr) |
| 110 | { |
| 111 | } |
| 112 | |
| 113 | #endif |
| 114 | |
| 115 | #ifdef CONFIG_PROC_FS |
| 116 | |
| 117 | #ifdef MAX_DMA_CHANNELS |
| 118 | static int proc_dma_show(struct seq_file *m, void *v) |
| 119 | { |
| 120 | int i; |
| 121 | |
| 122 | for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) { |
| 123 | if (dma_chan_busy[i].lock) { |
| 124 | seq_printf(m, "%2d: %s\n", i, |
| 125 | dma_chan_busy[i].device_id); |
| 126 | } |
| 127 | } |
| 128 | return 0; |
| 129 | } |
| 130 | #else |
| 131 | static int proc_dma_show(struct seq_file *m, void *v) |
| 132 | { |
| 133 | seq_puts(m, "No DMA\n"); |
| 134 | return 0; |
| 135 | } |
| 136 | #endif /* MAX_DMA_CHANNELS */ |
| 137 | |
| 138 | static int proc_dma_open(struct inode *inode, struct file *file) |
| 139 | { |
| 140 | return single_open(file, proc_dma_show, NULL); |
| 141 | } |
| 142 | |
Helge Deller | 15ad7cd | 2006-12-06 20:40:36 -0800 | [diff] [blame] | 143 | static const struct file_operations proc_dma_operations = { |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 144 | .open = proc_dma_open, |
| 145 | .read = seq_read, |
| 146 | .llseek = seq_lseek, |
| 147 | .release = single_release, |
| 148 | }; |
| 149 | |
| 150 | static int __init proc_dma_init(void) |
| 151 | { |
| 152 | struct proc_dir_entry *e; |
| 153 | |
| 154 | e = create_proc_entry("dma", 0, NULL); |
| 155 | if (e) |
| 156 | e->proc_fops = &proc_dma_operations; |
| 157 | |
| 158 | return 0; |
| 159 | } |
| 160 | |
| 161 | __initcall(proc_dma_init); |
| 162 | #endif |
| 163 | |
| 164 | EXPORT_SYMBOL(request_dma); |
| 165 | EXPORT_SYMBOL(free_dma); |
| 166 | EXPORT_SYMBOL(dma_spin_lock); |