linux-kernel - [PATCH 2/4] spi: spi-fsl-dspi: Fix incorrect DMA setup

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Date:   Thu, 17 Nov 2016 17:46:49 +0530
From:   Sanchayan Maity <maitysanchayan@...il.com>
To:     broonie@...nel.org
Cc:     stefan@...er.ch, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
        Sanchayan Maity <maitysanchayan@...il.com>
Subject: [PATCH 2/4] spi: spi-fsl-dspi: Fix incorrect DMA setup

Currently dmaengine_prep_slave_single was being called with length
set to the complete DMA buffer size. This resulted in unwanted bytes
being transferred to the SPI register leading to clock and MOSI lines
having unwanted data even after chip select got deasserted and the
required bytes having been transferred.

Signed-off-by: Sanchayan Maity <maitysanchayan@...il.com>
---
 drivers/spi/spi-fsl-dspi.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi-fsl-dspi.c b/drivers/spi/spi-fsl-dspi.c
index b1ee1f5..aee8c88 100644
--- a/drivers/spi/spi-fsl-dspi.c
+++ b/drivers/spi/spi-fsl-dspi.c
@@ -265,7 +265,10 @@ static int dspi_next_xfer_dma_submit(struct fsl_dspi *dspi)
 
 	dma->tx_desc = dmaengine_prep_slave_single(dma->chan_tx,
 					dma->tx_dma_phys,
-					DSPI_DMA_BUFSIZE, DMA_MEM_TO_DEV,
+					dma->curr_xfer_len *
+					DMA_SLAVE_BUSWIDTH_4_BYTES /
+					(tx_word ? 2 : 1),
+					DMA_MEM_TO_DEV,
 					DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
 	if (!dma->tx_desc) {
 		dev_err(dev, "Not able to get desc for DMA xfer\n");
@@ -281,7 +284,10 @@ static int dspi_next_xfer_dma_submit(struct fsl_dspi *dspi)
 
 	dma->rx_desc = dmaengine_prep_slave_single(dma->chan_rx,
 					dma->rx_dma_phys,
-					DSPI_DMA_BUFSIZE, DMA_DEV_TO_MEM,
+					dma->curr_xfer_len *
+					DMA_SLAVE_BUSWIDTH_4_BYTES /
+					(tx_word ? 2 : 1),
+					DMA_DEV_TO_MEM,
 					DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
 	if (!dma->rx_desc) {
 		dev_err(dev, "Not able to get desc for DMA xfer\n");
-- 
2.10.2