kernel/dma.c

22689 /* $Id: dma.c,v 1.7 1994/12/28 03:35:33 root Exp root $
22690  * linux/kernel/dma.c: A DMA channel allocator. Inspired
22691  * by linux/kernel/irq.c.
22692  *
22693  * Written by Hennus Bergman, 1992.
22694  *
22695  * 1994/12/26: Changes by Alex Nash to fix a minor bug in
22696  * /proc/dma.  In the previous version the reported
22697  * device could end up being wrong, if a device requested
22698  * a DMA channel that was already in use.  [It also
22699  * happened to remove the sizeof(char *) == sizeof(int)
22700  * assumption introduced because of those /proc/dma
22701  * patches. -- Hennus]
22702  */
22703 
22704 #include <linux/kernel.h>
22705 #include <linux/errno.h>
22706 #include <asm/dma.h>
22707 #include <asm/system.h>
22708 #include <asm/spinlock.h>
22709 
22710 /* A note on resource allocation:
22711  *
22712  * All drivers needing DMA channels, should allocate and
22713  * release them through the public routines
22714  * `request_dma()' and `free_dma()'.
22715  *
22716  * In order to avoid problems, all processes should
22717  * allocate resources in the same sequence and release
22718  * them in the reverse order.
22719  *
22720  * So, when allocating DMAs and IRQs, first allocate the
22721  * IRQ, then the DMA.  When releasing them, first release
22722  * the DMA, then release the IRQ.  If you don't, you may
22723  * cause allocation requests to fail unnecessarily.  This
22724  * doesn't really matter now, but it will once we get
22725  * real semaphores in the kernel.  */
22726 
22727 spinlock_t dma_spin_lock = SPIN_LOCK_UNLOCKED;
22728 
22729 /* Channel n is busy iff dma_chan_busy[n].lock != 0.
22730  * DMA0 used to be reserved for DRAM refresh, but
22731  * apparently not any more...  DMA4 is reserved for
22732  * cascading.  */
22733 struct dma_chan {
22734   int  lock;
22735   const char *device_id;
22736 };
22737 
22738 static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] ={
22739   { 0, 0 },
22740   { 0, 0 },
22741   { 0, 0 },
22742   { 0, 0 },
22743   { 1, "cascade" },
22744   { 0, 0 },
22745   { 0, 0 },
22746   { 0, 0 }
22747 };
22748 
22749 int get_dma_list(char *buf)
22750 {
22751   int i, len = 0;
22752 
22753   for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) {
22754     if (dma_chan_busy[i].lock) {
22755         len += sprintf(buf+len, "%2d: %s\n",
22756            i,
22757            dma_chan_busy[i].device_id);
22758     }
22759   }
22760   return len;
22761 } /* get_dma_list */
22762 
22763 
22764 int request_dma(unsigned int dmanr,
22765                 const char * device_id)
22766 {
22767   if (dmanr >= MAX_DMA_CHANNELS)
22768     return -EINVAL;
22769 
22770   if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0)
22771     return -EBUSY;
22772 
22773   dma_chan_busy[dmanr].device_id = device_id;
22774 
22775   /* old flag was 0, now contains 1 to indicate busy */
22776   return 0;
22777 } /* request_dma */
22778 
22779 
22780 void free_dma(unsigned int dmanr)
22781 {
22782   if (dmanr >= MAX_DMA_CHANNELS) {
22783     printk("Trying to free DMA%d\n", dmanr);
22784     return;
22785   }
22786 
22787   if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) {
22788     printk("Trying to free free DMA%d\n", dmanr);
22789     return;
22790   }
22791 
22792 } /* free_dma */