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Subject[PATCH v3 1/2] spi: Add DMA support for spi_flash_read()
Date
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@ti.com>
---

v3: No changes.
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 77e6e45951f4..da2cbe205654 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 1f03483f61e5..7b53af4ba5f8 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -1143,6 +1143,8 @@ 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;
@@ -1155,6 +1157,8 @@ 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 */
--
2.8.3
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