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

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On 16-11-17 17:03:19, Stefan Agner wrote:
> On 2016-11-17 04:16, Sanchayan Maity wrote:
> > 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@xxxxxxxxx>
> > ---
> >  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,
> 
> Hm, this is getting ridiculous, I think we convert curr_xfer_len from
> bytes to DMA transfers in almost every use.
> 
> Can we make it be transfer length in actual 4 byte transfers? We then
> probably have to convert it to bytes once to subtract from
> curr_remaining_bytes, but I think it would simplify code overall...

Will the below be acceptable fix?

diff --git a/drivers/spi/spi-fsl-dspi.c b/drivers/spi/spi-fsl-dspi.c
index 41422cd..db7f091 100644
--- a/drivers/spi/spi-fsl-dspi.c
+++ b/drivers/spi/spi-fsl-dspi.c
@@ -217,15 +217,13 @@ static void dspi_rx_dma_callback(void *arg)
        struct fsl_dspi *dspi = arg;
        struct fsl_dspi_dma *dma = dspi->dma;
        int rx_word;
-       int i, len;
+       int i;
        u16 d;
 
        rx_word = is_double_byte_mode(dspi);
 
-       len = rx_word ? (dma->curr_xfer_len / 2) : dma->curr_xfer_len;
-
        if (!(dspi->dataflags & TRAN_STATE_RX_VOID)) {
-               for (i = 0; i < len; i++) {
+               for (i = 0; i < dma->curr_xfer_len; i++) {
                        d = dspi->dma->rx_dma_buf[i];
                        rx_word ? (*(u16 *)dspi->rx = d) :
                                                (*(u8 *)dspi->rx = d);
@@ -242,14 +240,12 @@ static int dspi_next_xfer_dma_submit(struct fsl_dspi *dspi)
        struct device *dev = &dspi->pdev->dev;
        int time_left;
        int tx_word;
-       int i, len;
+       int i;
        u16 val;
 
        tx_word = is_double_byte_mode(dspi);
 
-       len = tx_word ? (dma->curr_xfer_len / 2) : dma->curr_xfer_len;
-
-       for (i = 0; i < len - 1; i++) {
+       for (i = 0; i < dma->curr_xfer_len - 1; i++) {
                val = tx_word ? *(u16 *) dspi->tx : *(u8 *) dspi->tx;
                dspi->dma->tx_dma_buf[i] =
                        SPI_PUSHR_TXDATA(val) | SPI_PUSHR_PCS(dspi->cs) |
@@ -267,7 +263,9 @@ 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,
+                                       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");
@@ -283,7 +281,9 @@ 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,
+                                       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");
@@ -330,17 +330,17 @@ static int dspi_dma_xfer(struct fsl_dspi *dspi)
        struct device *dev = &dspi->pdev->dev;
        int curr_remaining_bytes;
        int bytes_per_buffer;
-       int tx_word;
+       int tx_word = 1;
        int ret = 0;
 
-       tx_word = is_double_byte_mode(dspi);
+       if (is_double_byte_mode(dspi))
+               tx_word = 2;
        curr_remaining_bytes = dspi->len;
+       bytes_per_buffer = DSPI_DMA_BUFSIZE / DSPI_FIFO_SIZE;
        while (curr_remaining_bytes) {
                /* Check if current transfer fits the DMA buffer */
-               dma->curr_xfer_len = curr_remaining_bytes;
-               bytes_per_buffer = DSPI_DMA_BUFSIZE /
-                               (DSPI_FIFO_SIZE / (tx_word ? 2 : 1));
-               if (curr_remaining_bytes > bytes_per_buffer)
+               dma->curr_xfer_len = curr_remaining_bytes / tx_word;
+               if (dma->curr_xfer_len > bytes_per_buffer)
                        dma->curr_xfer_len = bytes_per_buffer;
 
                ret = dspi_next_xfer_dma_submit(dspi);
@@ -349,7 +349,7 @@ static int dspi_dma_xfer(struct fsl_dspi *dspi)
                        goto exit;
 
                } else {
-                       curr_remaining_bytes -= dma->curr_xfer_len;
+                       curr_remaining_bytes -= dma->curr_xfer_len * tx_word;
                        if (curr_remaining_bytes < 0)
                                curr_remaining_bytes = 0;
                        dspi->len = curr_remaining_bytes;


Regards,
Sanchayan.
> 
> --
> Stefan
> 
> 
> >  					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");
--
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