FreeBSD/Linux Kernel Cross Reference
sys/kernel/dma.c

     /*
      * 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\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)
   {
           proc_create("dma", 0, NULL, &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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