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

/*
 * First make the LLIs (could/should we do this earlier??)
 * slave (m/p) - no queued transactions allowed at present
 *	TODO allow queued transactions for non circular buffers
 * Set up the channel active txd as inactive
 * m2m	- transactions may be queued
 * If no active txd on channel
 *	set it up as inactive
 *	- issue_pending() will set active & start
 * else
 *	queue it
 * Lock channel since there may be (at least for m2m) multiple calls
 *
 * Return < 0 for error
 */
static dma_cookie_t pl08x_tx_submit(struct dma_async_tx_descriptor *tx)
{
	int num_llis;
	unsigned long flags;
	struct pl08x_txd *local_txd = container_of(tx, struct pl08x_txd, tx);
	struct pl08x_dma_chan *local_chan =
			container_of(tx->chan, struct pl08x_dma_chan, chan);
	int pl08x_chan_num = local_chan->chan_id;
	num_llis = fill_LLIS_for_desc(local_txd, pl08x_chan_num);

	if (num_llis) {
		spin_lock_irqsave(&local_chan->lock, flags);
		atomic_inc(&local_chan->last_issued);
		tx->cookie = atomic_read(&local_chan->last_issued);

		if (local_chan->at) {

			/*
			 * If this device not using a circular buffer then
			 * queue this new descriptor.
			 * The descriptor for a circular buffer continues
			 * to be used until the channel is freed
			 */
			if (local_txd->pcd->circular_buffer)
				dev_err(&pd.dmac->dev,
					"%s - attempting to queue a circular buffer\n",
						__func__);
			else
				list_add_tail(&local_txd->txd_list,
					&local_chan->desc_list);

		} else {
			local_txd->slave = local_chan->slave;
			local_chan->at = local_txd;
			local_txd->active = 0;
		}

		spin_unlock_irqrestore(&local_chan->lock, flags);

		return tx->cookie;
	} else
		return -EINVAL;
}