mmc: jz4740: prepare next dma transfer in parallel with current transfer

Make use of the MMC asynchronous request capability to prepare the
next DMA transfer request in parallel with the current transfer.
This is done by adding pre-request and post-request callbacks that are
used by the MMC framework during an active data transfer.

It should help reduce the impact of DMA preparation overhead on the SD
card performance.
Signed-off-by: Apelete Seketeli <apelete@seketeli.net>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/jz4740_mmc.c

@@ -114,6 +114,11 @@ enum jz4740_mmc_state {
 	JZ4740_MMC_STATE_DONE,
 };
 
+struct jz4740_mmc_host_next {
+	int sg_len;
+	s32 cookie;
+};
+
 struct jz4740_mmc_host {
 	struct mmc_host *mmc;
 	struct platform_device *pdev;
@@ -143,6 +148,7 @@ struct jz4740_mmc_host {
 	/* DMA support */
 	struct dma_chan *dma_rx;
 	struct dma_chan *dma_tx;
+	struct jz4740_mmc_host_next next_data;
 	bool use_dma;
 	int sg_len;
 
@@ -184,6 +190,9 @@ static int jz4740_mmc_acquire_dma_channels(struct jz4740_mmc_host *host)
 		goto free_master_write;
 	}
 
+	/* Initialize DMA pre request cookie */
+	host->next_data.cookie = 1;
+
 	return 0;
 
 free_master_write:
@@ -196,23 +205,72 @@ static inline int jz4740_mmc_get_dma_dir(struct mmc_data *data)
 	return (data->flags & MMC_DATA_READ) ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
 }
 
+static inline struct dma_chan *jz4740_mmc_get_dma_chan(struct jz4740_mmc_host *host,
+						       struct mmc_data *data)
+{
+	return (data->flags & MMC_DATA_READ) ? host->dma_rx : host->dma_tx;
+}
+
 static void jz4740_mmc_dma_unmap(struct jz4740_mmc_host *host,
 				 struct mmc_data *data)
 {
-	struct dma_chan *chan;
+	struct dma_chan *chan = jz4740_mmc_get_dma_chan(host, data);
 	enum dma_data_direction dir = jz4740_mmc_get_dma_dir(data);
 
-	if (dir == DMA_TO_DEVICE)
-		chan = host->dma_tx;
-	else
-		chan = host->dma_rx;
-
 	dma_unmap_sg(chan->device->dev, data->sg, data->sg_len, dir);
 }
 
+/* Prepares DMA data for current/next transfer, returns non-zero on failure */
+static int jz4740_mmc_prepare_dma_data(struct jz4740_mmc_host *host,
+				       struct mmc_data *data,
+				       struct jz4740_mmc_host_next *next,
+				       struct dma_chan *chan)
+{
+	struct jz4740_mmc_host_next *next_data = &host->next_data;
+	enum dma_data_direction dir = jz4740_mmc_get_dma_dir(data);
+	int sg_len;
+
+	if (!next && data->host_cookie &&
+	    data->host_cookie != host->next_data.cookie) {
+		dev_warn(mmc_dev(host->mmc),
+			 "[%s] invalid cookie: data->host_cookie %d host->next_data.cookie %d\n",
+			 __func__,
+			 data->host_cookie,
+			 host->next_data.cookie);
+		data->host_cookie = 0;
+	}
+
+	/* Check if next job is already prepared */
+	if (next || data->host_cookie != host->next_data.cookie) {
+		sg_len = dma_map_sg(chan->device->dev,
+				    data->sg,
+				    data->sg_len,
+				    dir);
+
+	} else {
+		sg_len = next_data->sg_len;
+		next_data->sg_len = 0;
+	}
+
+	if (sg_len <= 0) {
+		dev_err(mmc_dev(host->mmc),
+			"Failed to map scatterlist for DMA operation\n");
+		return -EINVAL;
+	}
+
+	if (next) {
+		next->sg_len = sg_len;
+		data->host_cookie = ++next->cookie < 0 ? 1 : next->cookie;
+	} else
+		host->sg_len = sg_len;
+
+	return 0;
+}
+
 static int jz4740_mmc_start_dma_transfer(struct jz4740_mmc_host *host,
 					 struct mmc_data *data)
 {
+	int ret;
 	struct dma_chan *chan;
 	struct dma_async_tx_descriptor *desc;
 	struct dma_slave_config conf = {
@@ -221,9 +279,8 @@ static int jz4740_mmc_start_dma_transfer(struct jz4740_mmc_host *host,
 		.src_maxburst = JZ4740_MMC_FIFO_HALF_SIZE,
 		.dst_maxburst = JZ4740_MMC_FIFO_HALF_SIZE,
 	};
-	enum dma_data_direction dir = jz4740_mmc_get_dma_dir(data);
 
-	if (dir == DMA_TO_DEVICE) {
+	if (data->flags & MMC_DATA_WRITE) {
 		conf.direction = DMA_MEM_TO_DEV;
 		conf.dst_addr = host->mem_res->start + JZ_REG_MMC_TXFIFO;
 		conf.slave_id = JZ4740_DMA_TYPE_MMC_TRANSMIT;
@@ -235,16 +292,9 @@ static int jz4740_mmc_start_dma_transfer(struct jz4740_mmc_host *host,
 		chan = host->dma_rx;
 	}
 
-	host->sg_len = dma_map_sg(chan->device->dev,
-				  data->sg,
-				  data->sg_len,
-				  dir);
-
-	if (host->sg_len == 0) {
-		dev_err(mmc_dev(host->mmc),
-			"Failed to map scatterlist for DMA operation\n");
-		return -EINVAL;
-	}
+	ret = jz4740_mmc_prepare_dma_data(host, data, NULL, chan);
+	if (ret)
+		return ret;
 
 	dmaengine_slave_config(chan, &conf);
 	desc = dmaengine_prep_slave_sg(chan,
@@ -269,6 +319,43 @@ static int jz4740_mmc_start_dma_transfer(struct jz4740_mmc_host *host,
 	return -ENOMEM;
 }
 
+static void jz4740_mmc_pre_request(struct mmc_host *mmc,
+				   struct mmc_request *mrq,
+				   bool is_first_req)
+{
+	struct jz4740_mmc_host *host = mmc_priv(mmc);
+	struct mmc_data *data = mrq->data;
+	struct jz4740_mmc_host_next *next_data = &host->next_data;
+
+	BUG_ON(data->host_cookie);
+
+	if (host->use_dma) {
+		struct dma_chan *chan = jz4740_mmc_get_dma_chan(host, data);
+
+		if (jz4740_mmc_prepare_dma_data(host, data, next_data, chan))
+			data->host_cookie = 0;
+	}
+}
+
+static void jz4740_mmc_post_request(struct mmc_host *mmc,
+				    struct mmc_request *mrq,
+				    int err)
+{
+	struct jz4740_mmc_host *host = mmc_priv(mmc);
+	struct mmc_data *data = mrq->data;
+
+	if (host->use_dma && data->host_cookie) {
+		jz4740_mmc_dma_unmap(host, data);
+		data->host_cookie = 0;
+	}
+
+	if (err) {
+		struct dma_chan *chan = jz4740_mmc_get_dma_chan(host, data);
+
+		dmaengine_terminate_all(chan);
+	}
+}
+
 /*----------------------------------------------------------------------------*/
 
 static void jz4740_mmc_set_irq_enabled(struct jz4740_mmc_host *host,
@@ -627,14 +714,19 @@ static irqreturn_t jz_mmc_irq_worker(int irq, void *devid)
 
 	case JZ4740_MMC_STATE_TRANSFER_DATA:
 		if (host->use_dma) {
-			/* Use DMA if enabled, data transfer direction was
-			 * defined  before in jz_mmc_prepare_data_transfer().
+			/* Use DMA if enabled.
+			 * Data transfer direction is defined later by
+			 * relying on data flags in
+			 * jz4740_mmc_prepare_dma_data() and
+			 * jz4740_mmc_start_dma_transfer().
 			 */
 			timeout = jz4740_mmc_start_dma_transfer(host, data);
 			data->bytes_xfered = data->blocks * data->blksz;
 		} else if (data->flags & MMC_DATA_READ)
-			/* If DMA is not enabled, rely on data flags
-			 * to establish data transfer direction.
+			/* Use PIO if DMA is not enabled.
+			 * Data transfer direction was defined before
+			 * by relying on data flags in
+			 * jz_mmc_prepare_data_transfer().
 			 */
 			timeout = jz4740_mmc_read_data(host, data);
 		else
@@ -809,6 +901,8 @@ static void jz4740_mmc_enable_sdio_irq(struct mmc_host *mmc, int enable)
 
 static const struct mmc_host_ops jz4740_mmc_ops = {
 	.request	= jz4740_mmc_request,
+	.pre_req	= jz4740_mmc_pre_request,
+	.post_req	= jz4740_mmc_post_request,
 	.set_ios	= jz4740_mmc_set_ios,
 	.get_ro		= mmc_gpio_get_ro,
 	.get_cd		= mmc_gpio_get_cd,