spi: Provide core support for DMA mapping transfers

The process of DMA mapping buffers for SPI transfers does not vary between
devices so in order to save duplication of code in drivers this can be
factored out into the core, allowing it to be integrated with the work that
is being done on factoring out the common elements from the data path
including more sharing of dmaengine code.

In order to use this masters need to provide a can_dma() operation and while
the hardware is prepared they should ensure that DMA channels are provided
in tx_dma and rx_dma. The core will then ensure that the buffers are mapped
for DMA prior to calling transfer_one_message().

Currently the cleanup on error is not complete, this needs to be improved.

Signed-off-by: Mark Brown <broonie@linaro.org>

Author: broonie

drivers/spi/spi.c

@@ -24,6 +24,8 @@
 #include <linux/device.h>
 #include <linux/init.h>
 #include <linux/cache.h>
+#include <linux/dma-mapping.h>
+#include <linux/dmaengine.h>
 #include <linux/mutex.h>
 #include <linux/of_device.h>
 #include <linux/of_irq.h>
@@ -580,6 +582,77 @@ static void spi_set_cs(struct spi_device *spi, bool enable)
 		spi->master->set_cs(spi, !enable);
 }
 
+static int spi_map_msg(struct spi_master *master, struct spi_message *msg)
+{
+	struct device *dev = master->dev.parent;
+	struct device *tx_dev, *rx_dev;
+	struct spi_transfer *xfer;
+
+	if (msg->is_dma_mapped || !master->can_dma)
+		return 0;
+
+	tx_dev = &master->dma_tx->dev->device;
+	rx_dev = &master->dma_rx->dev->device;
+
+	list_for_each_entry(xfer, &msg->transfers, transfer_list) {
+		if (!master->can_dma(master, msg->spi, xfer))
+			continue;
+
+		if (xfer->tx_buf != NULL) {
+			xfer->tx_dma = dma_map_single(tx_dev,
+						      (void *)xfer->tx_buf,
+						      xfer->len,
+						      DMA_TO_DEVICE);
+			if (dma_mapping_error(dev, xfer->tx_dma)) {
+				dev_err(dev, "dma_map_single Tx failed\n");
+				return -ENOMEM;
+			}
+		}
+
+		if (xfer->rx_buf != NULL) {
+			xfer->rx_dma = dma_map_single(rx_dev,
+						      xfer->rx_buf, xfer->len,
+						      DMA_FROM_DEVICE);
+			if (dma_mapping_error(dev, xfer->rx_dma)) {
+				dev_err(dev, "dma_map_single Rx failed\n");
+				dma_unmap_single(tx_dev, xfer->tx_dma,
+						 xfer->len, DMA_TO_DEVICE);
+				return -ENOMEM;
+			}
+		}
+	}
+
+	master->cur_msg_mapped = true;
+
+	return 0;
+}
+
+static int spi_unmap_msg(struct spi_master *master, struct spi_message *msg)
+{
+	struct spi_transfer *xfer;
+	struct device *tx_dev, *rx_dev;
+
+	if (!master->cur_msg_mapped || msg->is_dma_mapped || !master->can_dma)
+		return 0;
+
+	tx_dev = &master->dma_tx->dev->device;
+	rx_dev = &master->dma_rx->dev->device;
+
+	list_for_each_entry(xfer, &msg->transfers, transfer_list) {
+		if (!master->can_dma(master, msg->spi, xfer))
+			continue;
+
+		if (xfer->rx_buf)
+			dma_unmap_single(rx_dev, xfer->rx_dma, xfer->len,
+					 DMA_FROM_DEVICE);
+		if (xfer->tx_buf)
+			dma_unmap_single(tx_dev, xfer->tx_dma, xfer->len,
+					 DMA_TO_DEVICE);
+	}
+
+	return 0;
+}
+
 /*
  * spi_transfer_one_message - Default implementation of transfer_one_message()
  *
@@ -752,6 +825,13 @@ static void spi_pump_messages(struct kthread_work *work)
 		master->cur_msg_prepared = true;
 	}
 
+	ret = spi_map_msg(master, master->cur_msg);
+	if (ret) {
+		master->cur_msg->status = ret;
+		spi_finalize_current_message(master);
+		return;
+	}
+
 	ret = master->transfer_one_message(master, master->cur_msg);
 	if (ret) {
 		dev_err(&master->dev,
@@ -841,6 +921,8 @@ void spi_finalize_current_message(struct spi_master *master)
 	queue_kthread_work(&master->kworker, &master->pump_messages);
 	spin_unlock_irqrestore(&master->queue_lock, flags);
 
+	spi_unmap_msg(master, mesg);
+
 	if (master->cur_msg_prepared && master->unprepare_message) {
 		ret = master->unprepare_message(master, mesg);
 		if (ret) {

include/linux/spi/spi.h

@@ -25,6 +25,8 @@
 #include <linux/kthread.h>
 #include <linux/completion.h>
 
+struct dma_chan;
+
 /*
  * INTERFACES between SPI master-side drivers and SPI infrastructure.
  * (There's no SPI slave support for Linux yet...)
@@ -386,6 +388,17 @@ struct spi_master {
 	/* called on release() to free memory provided by spi_master */
 	void			(*cleanup)(struct spi_device *spi);
 
+	/*
+	 * Used to enable core support for DMA handling, if can_dma()
+	 * exists and returns true then the transfer will be mapped
+	 * prior to transfer_one() being called.  The driver should
+	 * not modify or store xfer and dma_tx and dma_rx must be set
+	 * while the device is prepared.
+	 */
+	bool			(*can_dma)(struct spi_master *master,
+					   struct spi_device *spi,
+					   struct spi_transfer *xfer);
+
 	/*
 	 * These hooks are for drivers that want to use the generic
 	 * master transfer queueing mechanism. If these are used, the
@@ -404,6 +417,7 @@ struct spi_master {
 	bool				rt;
 	bool				auto_runtime_pm;
 	bool                            cur_msg_prepared;
+	bool				cur_msg_mapped;
 	struct completion               xfer_completion;
 
 	int (*prepare_transfer_hardware)(struct spi_master *master);
@@ -425,6 +439,10 @@ struct spi_master {
 
 	/* gpio chip select */
 	int			*cs_gpios;
+
+	/* DMA channels for use with core dmaengine helpers */
+	struct dma_chan		*dma_tx;
+	struct dma_chan		*dma_rx;
 };
 
 static inline void *spi_master_get_devdata(struct spi_master *master)