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

/*
 * Slave transactions callback to the slave device to allow
 * synchronization of slave DMA signals with the DMAC enable
 */
static void pl08x_issue_pending(struct dma_chan *chan)
{
	struct pl08x_dma_chan *local_chan
		= container_of(chan, struct pl08x_dma_chan, chan);
	int pl08x_chan_num = local_chan->chan_id;

	if (local_chan->at) {
		if (!local_chan->at->active) {
			pl08x_set_cregs(local_chan->at, local_chan->chan_id);
			if (local_chan->slave) {
				/*
				 * Allow slaves to activate signals
				 * concurrent to the DMAC enable
				 */
				if (local_chan->at->tx.callback) {
					((struct pl08x_callback_param *)
						local_chan->at->tx.callback_param)->act =
								PL08X_SIGNAL_START;
					local_chan->at->tx.callback(
						local_chan->at->tx.callback_param);
				}
			}
			pl08x_enable_dmac_chan(local_chan->chan_id);
			local_chan->at->active = 1;
		}
		/*
		 * else skip active transfer
		 * Calls with active txd occur for NET_DMA
		 * - there can be queued descriptors
		 */
	}
	/*
	 * else - calls with no active descriptor occur for NET_DMA
	 */
}