// SPDX-License-Identifier: GPL-2.0

  /*

   * 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/export.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>

  
  /* 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
  ", dmanr);
  		return;
  	}
  
  	if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) {
  		printk(KERN_WARNING "Trying to free free DMA%d
  ", 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
  ", 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
  ");
  	return 0;
  }
  #endif /* MAX_DMA_CHANNELS */

  static int __init proc_dma_init(void)
  {

  	proc_create_single("dma", 0, NULL, proc_dma_show);

  	return 0;
  }
  
  __initcall(proc_dma_init);
  #endif
  
  EXPORT_SYMBOL(request_dma);
  EXPORT_SYMBOL(free_dma);
  EXPORT_SYMBOL(dma_spin_lock);