[PATCH 18/18] mtd: rawnand: gpmi: issue two commands in a single DMA chain

[Sam Lefebvre <sam.lefebvre@essensium.com>]

gpmi_nand_command() may issue two commands. Instead of issuing them as
separate DMAs, chain them together and issue only a single DMA.

This removes one DMA interrupt and associated overhead. For full-page
reads with ECC, it reduces the number of interrupts from 4 per page to
3 per page (2 DMA interrupts + 1 BCH interrupt).

Signed-off-by: Sam Lefebvre <sam.lefebvre@essensium.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
---
 drivers/mtd/nand/raw/gpmi-nand/gpmi-lib.c  | 12 +++++++-----
 drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c |  8 +++++---
 drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.h |  2 +-
 3 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/drivers/mtd/nand/raw/gpmi-nand/gpmi-lib.c b/drivers/mtd/nand/raw/gpmi-nand/gpmi-lib.c
index 46b2208df30e..8f5a2a242228 100644
--- a/drivers/mtd/nand/raw/gpmi-nand/gpmi-lib.c
+++ b/drivers/mtd/nand/raw/gpmi-nand/gpmi-lib.c
@@ -549,12 +549,12 @@ int gpmi_is_ready(struct gpmi_nand_data *this, unsigned chip)
 }
 
 int gpmi_send_command(struct gpmi_nand_data *this, struct scatterlist *sgl,
-		      unsigned int command_length)
+		      unsigned int command_length, bool chain, bool start_dma)
 {
 	struct dma_chan *channel = get_dma_chan(this);
 	struct dma_async_tx_descriptor *desc;
 	int chip = this->current_chip;
-	int ret;
+	int ret = 0;
 	u32 pio[3];
 
 	/* [1] send out the PIO words */
@@ -568,7 +568,8 @@ int gpmi_send_command(struct gpmi_nand_data *this, struct scatterlist *sgl,
 	pio[1] = pio[2] = 0;
 	desc = dmaengine_prep_slave_sg(channel,
 					(struct scatterlist *)pio,
-					ARRAY_SIZE(pio), DMA_TRANS_NONE, 0);
+					ARRAY_SIZE(pio), DMA_TRANS_NONE,
+					chain ? DMA_PREP_INTERRUPT : 0);
 	if (!desc)
 		return -EINVAL;
 
@@ -579,8 +580,9 @@ int gpmi_send_command(struct gpmi_nand_data *this, struct scatterlist *sgl,
 	if (!desc)
 		return -EINVAL;
 
-	/* [3] submit the DMA */
-	ret = start_dma_without_bch_irq(this, desc);
+	if (start_dma)
+		/* [3] submit the DMA */
+		ret = start_dma_without_bch_irq(this, desc);
 
 	return ret;
 }
diff --git a/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c b/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
index 4455ea428255..abf227148b01 100644
--- a/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
+++ b/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
@@ -1150,11 +1150,12 @@ static void gpmi_nand_command(struct mtd_info *mtd, unsigned int command,
 			break;
 		}
 
-	/* This starts the DMA for the command and waits for it to finish. */
+	/* Chain the two commands, start the DMA and wait for it to finish. */
 	if (this->command_length > 0) {
 		sg_init_one(&this->cmd_sgl, this->cmd_buffer, this->command_length);
 		dma_map_sg(this->dev, &this->cmd_sgl, 1, DMA_TO_DEVICE);
-		ret = gpmi_send_command(this, &this->cmd_sgl, this->command_length);
+		ret = gpmi_send_command(this, &this->cmd_sgl, this->command_length,
+					false, this->command_length2 == 0);
 		if (ret)
 			dev_err(this->dev, "Chip: %u, Error %d\n",
 				this->current_chip, ret);
@@ -1163,7 +1164,8 @@ static void gpmi_nand_command(struct mtd_info *mtd, unsigned int command,
 	if (this->command_length2 > 0) {
 		sg_init_one(&this->cmd_sgl2, this->cmd_buffer + 64, this->command_length2);
 		dma_map_sg(this->dev, &this->cmd_sgl2, 1, DMA_TO_DEVICE);
-		ret = gpmi_send_command(this, &this->cmd_sgl2, this->command_length2);
+		ret = gpmi_send_command(this, &this->cmd_sgl2, this->command_length2,
+					this->command_length > 0, true);
 		if (ret)
 			dev_err(this->dev, "Chip: %u, Error %d\n",
 				this->current_chip, ret);
diff --git a/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.h b/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.h
index 9dc3dd16fa0b..a09ec300754f 100644
--- a/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.h
+++ b/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.h
@@ -189,7 +189,7 @@ void gpmi_dump_info(struct gpmi_nand_data *);
 int bch_set_geometry(struct gpmi_nand_data *);
 int gpmi_is_ready(struct gpmi_nand_data *, unsigned chip);
 int gpmi_send_command(struct gpmi_nand_data *, struct scatterlist *sgl,
-		      unsigned int command_length);
+		      unsigned int command_length, bool chain, bool start_dma);
 int gpmi_enable_clk(struct gpmi_nand_data *this);
 int gpmi_disable_clk(struct gpmi_nand_data *this);
 int gpmi_setup_data_interface(struct mtd_info *mtd, int chipnr,
-- 
2.14.1