详解ARM的AMBA设备中的DMA设备PL08X的Linux驱动

第 3 章 ARM的PL08X的代码的详细解析 第三部分

/*
 * Code accessing dma_async_is_complete() in a tight loop
 * may give problems - could schedule where indicated.
 * If slaves are relying on interrupts to signal completion this
 * function must not be called with interrupts disabled
 */
static enum dma_status pl08x_dma_is_complete(struct dma_chan *chan,
						dma_cookie_t cookie,
						dma_cookie_t *done,
						dma_cookie_t *used)
{
	struct pl08x_dma_chan *local_chan = container_of(chan,
				struct pl08x_dma_chan, chan);
	dma_cookie_t last_used;
	dma_cookie_t last_complete;
	enum dma_status ret;

	last_used = atomic_read(&local_chan->last_issued);
	last_complete = local_chan->lc;

	if (done)
		*done = last_complete;
	if (used)
		*used = last_used;

	ret = dma_async_is_complete(cookie, last_complete, last_used);
	if (ret == DMA_SUCCESS)
		return ret;

	/*
	 * schedule(); could be inserted here
	 */

	/*
	 * This cookie not complete yet
	 */
	last_used = atomic_read(&local_chan->last_issued);
	last_complete = local_chan->lc;

	if (done)
		*done = last_complete;
	if (used)
		*used = last_used;

	return dma_async_is_complete(cookie, last_complete, last_used);
}