dma.c

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/*
 * 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" },
};


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 */

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);