Function isa_dma_init

freebsd/x86/isa/isa_dma.c:87–141

* Setup a DMA channel's bounce buffer. */

 * Setup a DMA channel's bounce buffer.
 */
int
isa_dma_init(int chan, u_int bouncebufsize, int flag)
{
	void *buf;
	int contig;

#ifdef DIAGNOSTIC
	if (chan & ~VALID_DMA_MASK)
		panic("isa_dma_init: channel out of range");
#endif

	/* Try malloc() first.  It works better if it works. */
	buf = malloc(bouncebufsize, M_DEVBUF, flag);
	if (buf != NULL) {
		if (isa_dmarangecheck(buf, bouncebufsize, chan) != 0) {
			free(buf, M_DEVBUF);
			buf = NULL;
		}
		contig = 0;
	}

	if (buf == NULL) {
		buf = contigmalloc(bouncebufsize, M_DEVBUF, flag, 0ul, 0xfffffful,
			   1ul, chan & 4 ? 0x20000ul : 0x10000ul);
		contig = 1;
	}

	if (buf == NULL)
		return (ENOMEM);

	mtx_lock(&isa_dma_lock);
	/*
	 * If a DMA channel is shared, both drivers have to call isa_dma_init
	 * since they don't know that the other driver will do it.
	 * Just return if we're already set up good.
	 * XXX: this only works if they agree on the bouncebuf size.  This
	 * XXX: is typically the case since they are multiple instances of
	 * XXX: the same driver.
	 */
	if (dma_bouncebuf[chan] != NULL) {
		if (contig)
			contigfree(buf, bouncebufsize, M_DEVBUF);
		else
			free(buf, M_DEVBUF);
		mtx_unlock(&isa_dma_lock);
		return (0);
	}

	dma_bouncebufsize[chan] = bouncebufsize;
	dma_bouncebuf[chan] = buf;

	mtx_unlock(&isa_dma_lock);

	return (0);
}

/*
 * Register a DMA channel's usage.  Usually called from a device driver