/* $Id: dma.c,v 1.1 1999/04/26 05:49:35 tb 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] */#define MACH_INCLUDE#include <linux/kernel.h>#include <linux/errno.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. *//* 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 }};#ifndef MACHintget_dma_list (char *buf){  int i, len = 0;    for (i = 0 ; i < MAX_DMA_CHANNELS ; i++)    {      if (dma_chan_busy[i].lock)	{	  len += linux_sprintf (buf+len, "%2d: %s\n",				i,				dma_chan_busy[i].device_id);	}    }  return len;} /* get_dma_list */#endifintrequest_dma (unsigned int dmanr, const char *device_id){  if (dmanr >= MAX_DMA_CHANNELS)    return -LINUX_EINVAL;    if (xchg (&dma_chan_busy[dmanr].lock, 1) != 0)    return -LINUX_EBUSY;    dma_chan_busy[dmanr].device_id = device_id;    /* old flag was 0, now contains 1 to indicate busy */  return 0;} /* request_dma */voidfree_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 */