linux-kernel - Re: [PATCH v2 3/4] spi: spi-fsl-dspi: Fix incorrect DMA setup

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Message-ID: <ac1daf304f9d250ca9602ae3a0f69193@agner.ch>
Date:   Mon, 21 Nov 2016 15:16:51 -0800
From:   Stefan Agner <stefan@...er.ch>
To:     Sanchayan Maity <maitysanchayan@...il.com>
Cc:     broonie@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org
Subject: Re: [PATCH v2 3/4] spi: spi-fsl-dspi: Fix incorrect DMA setup

On 2016-11-20 21:54, 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.
> 
> While at it also clean up the use of curr_xfer_len which is central
> to the DMA setup, from bytes to DMA transfers for every use.
> 
> Signed-off-by: Sanchayan Maity <maitysanchayan@...il.com>

Looks good to me:

Reviewed-by: Stefan Agner <stefan@...er.ch>

> ---
>  drivers/spi/spi-fsl-dspi.c | 35 ++++++++++++++++++-----------------
>  1 file changed, 18 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/spi/spi-fsl-dspi.c b/drivers/spi/spi-fsl-dspi.c
> index 41422cd..08882f7 100644
> --- a/drivers/spi/spi-fsl-dspi.c
> +++ b/drivers/spi/spi-fsl-dspi.c
> @@ -151,6 +151,7 @@ static const struct fsl_dspi_devtype_data ls2085a_data = {
>  };
>  
>  struct fsl_dspi_dma {
> +	/* Length of transfer in words of DSPI_FIFO_SIZE */
>  	u32 curr_xfer_len;
>  
>  	u32 *tx_dma_buf;
> @@ -217,15 +218,13 @@ 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 +241,12 @@ 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 +264,9 @@ 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 +282,9 @@ 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 +331,17 @@ 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 word = 1;
>  	int ret = 0;
>  
> -	tx_word = is_double_byte_mode(dspi);
> +	if (is_double_byte_mode(dspi))
> +		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 / 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 +350,7 @@ 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 * word;
>  			if (curr_remaining_bytes < 0)
>  				curr_remaining_bytes = 0;
>  			dspi->len = curr_remaining_bytes;