[PATCH v2 2/3] spi: Add DMA support for spi_flash_read()

[Vignesh R]

Few SPI devices provide accelerated read interfaces to read from
SPI-NOR flash devices. These hardwares also support DMA to transfer data
from flash to memory either via mem-to-mem DMA or dedicated slave DMA
channels. Hence, add support for DMA in order to improve throughput and
reduce CPU load.
Use spi_map_buf() to get sg table for the buffer and pass it to SPI
driver.

Signed-off-by: Vignesh R <vigneshr@xxxxxx>
---

v2: use cur_msg_mapped flag to indicate success/failure of spi_map_buf()

 drivers/spi/spi.c       | 14 ++++++++++++++
 include/linux/spi/spi.h |  4 ++++
 2 files changed, 18 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 82126bbe69cf..f98c19addc07 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -2725,6 +2725,7 @@ int spi_flash_read(struct spi_device *spi,
 
 {
 	struct spi_master *master = spi->master;
+	struct device *rx_dev = NULL;
 	int ret;
 
 	if ((msg->opcode_nbits == SPI_NBITS_DUAL ||
@@ -2750,9 +2751,22 @@ int spi_flash_read(struct spi_device *spi,
 			return ret;
 		}
 	}
+
 	mutex_lock(&master->bus_lock_mutex);
+	if (master->dma_rx) {
+		rx_dev = master->dma_rx->device->dev;
+		ret = spi_map_buf(master, rx_dev, &msg->rx_sg,
+				  msg->buf, msg->len,
+				  DMA_FROM_DEVICE);
+		if (!ret)
+			msg->cur_msg_mapped = true;
+	}
 	ret = master->spi_flash_read(spi, msg);
+	if (msg->cur_msg_mapped)
+		spi_unmap_buf(master, rx_dev, &msg->rx_sg,
+			      DMA_FROM_DEVICE);
 	mutex_unlock(&master->bus_lock_mutex);
+
 	if (master->auto_runtime_pm)
 		pm_runtime_put(master->dev.parent);
 
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 857a9a1d82b5..b51ea761b5c8 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -1141,6 +1141,8 @@ static inline ssize_t spi_w8r16be(struct spi_device *spi, u8 cmd)
  * @opcode_nbits: number of lines to send opcode
  * @addr_nbits: number of lines to send address
  * @data_nbits: number of lines for data
+ * @rx_sg: Scatterlist for receive data read from flash
+ * @cur_msg_mapped: message has been mapped for DMA
  */
 struct spi_flash_read_message {
 	void *buf;
@@ -1153,6 +1155,8 @@ struct spi_flash_read_message {
 	u8 opcode_nbits;
 	u8 addr_nbits;
 	u8 data_nbits;
+	struct sg_table rx_sg;
+	bool cur_msg_mapped;
 };
 
 /* SPI core interface for flash read support */
-- 
2.8.1