Re: [PATCH v3 2/3] spi: nxp-xspi: Improve AHB read performance with DMA

On Wed, Jul 22, 2026 at 05:00:43PM -0500, [email protected] wrote:
> From: Han Xu <[email protected]>
>
> Use eDMA for XSPI AHB read to improve the performance.
>
> Read with CPU
> root@imx943evk:~# dd if=/dev/mtd0 of=/dev/null bs=32M count=1
> 1+0 records in
> 1+0 records out
> 33554432 bytes (34 MB, 32 MiB) copied, 0.479719 s, 69.9 MB/s
>
> Read with DMA
> root@imx943evk:~# dd if=/dev/mtd0 of=/dev/null bs=32M count=1
> 1+0 records in
> 1+0 records out
> 33554432 bytes (34 MB, 32 MiB) copied, 0.115788 s, 290 MB/s
>
> Signed-off-by: Han Xu <[email protected]>
> ---

Reviewed-by: Frank Li <[email protected]>

>  drivers/spi/spi-nxp-xspi.c | 143 ++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 140 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/spi/spi-nxp-xspi.c b/drivers/spi/spi-nxp-xspi.c
> index 037eac24e6fd2..70cbc3ef658b6 100644
> --- a/drivers/spi/spi-nxp-xspi.c
> +++ b/drivers/spi/spi-nxp-xspi.c
> @@ -35,6 +35,8 @@
>  #include <linux/clk.h>
>  #include <linux/completion.h>
>  #include <linux/delay.h>
> +#include <linux/dmaengine.h>
> +#include <linux/dma-mapping.h>
>  #include <linux/err.h>
>  #include <linux/errno.h>
>  #include <linux/interrupt.h>
> @@ -303,6 +305,12 @@
>  	(opr)) << (((idx) % 2) * OPRND_SHIFT))
>
>  #define NXP_XSPI_MIN_IOMAP	SZ_4M
> +/*
> + * It takes 0.5s to access the entire area with DMA,
> + * leaving a 10x safety margin
> + */
> +#define NXP_XSPI_DMA_TOUT_MS	5000
> +#define NXP_XSPI_DMA_TOUT	msecs_to_jiffies(NXP_XSPI_DMA_TOUT_MS)
>  #define NXP_XSPI_MAX_CHIPSELECT		2
>  #define POLL_TOUT_US		5000
>
> @@ -336,6 +344,9 @@ struct nxp_xspi {
>  	/* mutex lock for each operation */
>  	struct mutex lock;
>  	int selected;
> +	int dma_copy_align;
> +	struct dma_chan *dma_rx;
> +	struct completion dma_rx_c;
>  #define XSPI_DTR_PROTO		BIT(0)
>  	int flags;
>  	/* Save the previous operation clock rate */
> @@ -796,6 +807,95 @@ static int nxp_xspi_ahb_read(struct nxp_xspi *xspi, const struct spi_mem_op *op)
>  	return 0;
>  }
>
> +static int nxp_xspi_dma_init(struct device *dev, struct nxp_xspi *xspi)
> +{
> +	struct dma_chan *rx;
> +
> +	rx = dma_request_chan(dev, "rx");
> +	if (IS_ERR(rx)) {
> +		int ret = PTR_ERR(rx);
> +
> +		if (ret == -EPROBE_DEFER)
> +			return ret;
> +		dev_dbg(dev, "NO DMA RX channel, falling back to CPU read\n");
> +		xspi->dma_copy_align = 1;
> +		return 0;
> +	}
> +
> +	xspi->dma_rx = rx;
> +	init_completion(&xspi->dma_rx_c);
> +	xspi->dma_copy_align = 1 << rx->device->copy_align;
> +
> +	return 0;
> +}
> +
> +static void nxp_xspi_dma_rx_callback(void *data)
> +{
> +	struct nxp_xspi *xspi = data;
> +
> +	complete(&xspi->dma_rx_c);
> +}
> +
> +static int nxp_xspi_ahb_dma_read(struct nxp_xspi *xspi,
> +				 const struct spi_mem_op *op)
> +{
> +	struct dma_async_tx_descriptor *desc;
> +	struct dma_chan *chan = xspi->dma_rx;
> +	unsigned long timeout;
> +	dma_addr_t src_addr, dst_addr;
> +	int ret = 0;
> +
> +	dst_addr = dma_map_single(chan->device->dev,
> +				  op->data.buf.in, op->data.nbytes,
> +				  DMA_FROM_DEVICE);
> +	if (dma_mapping_error(chan->device->dev, dst_addr)) {
> +		dev_err(xspi->dev, "failed to map DMA dst buffer\n");
> +		return -ENOMEM;
> +	}
> +
> +	src_addr = dma_map_resource(chan->device->dev,
> +				    (phys_addr_t)xspi->memmap_phy + op->addr.val,
> +				    op->data.nbytes,
> +				    DMA_TO_DEVICE, 0);
> +	if (dma_mapping_error(chan->device->dev, src_addr)) {
> +		dev_err(xspi->dev, "failed to map DMA src resource\n");
> +		ret = -ENOMEM;
> +		goto err_unmap_dst;
> +	}
> +
> +	desc = dmaengine_prep_dma_memcpy(chan, dst_addr, src_addr,
> +					 op->data.nbytes,
> +					 DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
> +	if (!desc) {
> +		dev_err(xspi->dev, "failed to prepare AHB RX DMA descriptor\n");
> +		ret = -EIO;
> +		goto err_unmap_src;
> +	}
> +
> +	desc->callback = nxp_xspi_dma_rx_callback;
> +	desc->callback_param = xspi;
> +	reinit_completion(&xspi->dma_rx_c);
> +	dmaengine_submit(desc);
> +	dma_async_issue_pending(chan);
> +
> +	timeout = wait_for_completion_timeout(&xspi->dma_rx_c, NXP_XSPI_DMA_TOUT);
> +	if (!timeout) {
> +		dev_err(xspi->dev, "AHB RX DMA timeout\n");
> +		dmaengine_terminate_sync(chan);
> +		ret = -ETIMEDOUT;
> +	}
> +
> +err_unmap_src:
> +	dma_unmap_resource(chan->device->dev, src_addr,
> +		op->data.nbytes, DMA_TO_DEVICE, 0);
> +
> +err_unmap_dst:
> +	dma_unmap_single(chan->device->dev, dst_addr,
> +			 op->data.nbytes, DMA_FROM_DEVICE);
> +
> +	return ret;
> +}
> +
>  static int nxp_xspi_fill_txfifo(struct nxp_xspi *xspi,
>  				 const struct spi_mem_op *op)
>  {
> @@ -1016,10 +1116,21 @@ static int nxp_xspi_exec_op(struct spi_mem *mem, const struct spi_mem_op *op)
>  	 *     all use IP write.
>  	 */
>  	if ((op->data.dir == SPI_MEM_DATA_IN) && !needs_ip_only(xspi)
> -		&& ((op->addr.val + op->data.nbytes) <= xspi->memmap_phy_size))
> -		err = nxp_xspi_ahb_read(xspi, op);
> -	else
> +		&& ((op->addr.val + op->data.nbytes) <= xspi->memmap_phy_size)) {
> +		/* use DMA for transfers no less than ahb_buf_size, when DMA is available */
> +		if (xspi->dma_rx && op->data.nbytes >= xspi->devtype_data->ahb_buf_size) {
> +			err = nxp_xspi_ahb_dma_read(xspi, op);
> +			if (err) {
> +				dev_warn_ratelimited(xspi->dev,
> +					"DMA read failed (%d), falling back to CPU read\n", err);
> +				err = nxp_xspi_ahb_read(xspi, op);
> +			}
> +		} else {
> +			err = nxp_xspi_ahb_read(xspi, op);
> +		}
> +	} else {
>  		err = nxp_xspi_do_op(xspi, op);
> +	}
>
>  	nxp_xspi_sw_reset(xspi);
>
> @@ -1029,6 +1140,7 @@ static int nxp_xspi_exec_op(struct spi_mem *mem, const struct spi_mem_op *op)
>  static int nxp_xspi_adjust_op_size(struct spi_mem *mem, struct spi_mem_op *op)
>  {
>  	struct nxp_xspi *xspi = spi_controller_get_devdata(mem->spi->controller);
> +	int alignment = xspi->dma_copy_align;
>
>  	if (op->data.dir == SPI_MEM_DATA_OUT) {
>  		if (op->data.nbytes > xspi->devtype_data->txfifo)
> @@ -1042,6 +1154,22 @@ static int nxp_xspi_adjust_op_size(struct spi_mem *mem, struct spi_mem_op *op)
>  		if (!needs_ip_only(xspi) && (op->addr.val < xspi->memmap_phy_size)
>  			&& ((op->addr.val + op->data.nbytes) > xspi->memmap_phy_size))
>  			op->data.nbytes = xspi->memmap_phy_size - op->addr.val;
> +
> +		/*
> +		 * For AHB DMA read, align the transfer to the DMA alignment
> +		 * boundaries. If the start address is unaligned, shorten this
> +		 * transfer so the next one starts on an aligned boundary.
> +		 * Otherwise, if the length is unaligned, round it down.
> +		 */
> +		if (xspi->dma_rx && !needs_ip_only(xspi) &&
> +		    (op->data.nbytes >= xspi->devtype_data->ahb_buf_size)) {
> +			if (op->addr.val & (alignment - 1))
> +				op->data.nbytes =
> +					ALIGN(op->addr.val, alignment) - op->addr.val;
> +			else if (op->data.nbytes & (alignment - 1))
> +				op->data.nbytes =
> +					ALIGN_DOWN(op->data.nbytes, alignment);
> +		}
>  	}
>
>  	return 0;
> @@ -1203,6 +1331,10 @@ static void nxp_xspi_cleanup(void *data)
>
>  	if (xspi->ahb_addr)
>  		iounmap(xspi->ahb_addr);
> +	if (xspi->dma_rx) {
> +		dmaengine_terminate_sync(xspi->dma_rx);
> +		dma_release_channel(xspi->dma_rx);
> +	}
>  }
>
>  static int nxp_xspi_probe(struct platform_device *pdev)
> @@ -1283,6 +1415,11 @@ static int nxp_xspi_probe(struct platform_device *pdev)
>  	if (ret)
>  		return ret;
>
> +	/* DMA is optional, failure(other than -EPROBE_DEFER) falls back to CPU */
> +	ret = nxp_xspi_dma_init(dev, xspi);
> +	if (ret == -EPROBE_DEFER)
> +		return ret;
> +
>  	ctlr->bus_num = -1;
>  	ctlr->num_chipselect = NXP_XSPI_MAX_CHIPSELECT;
>  	ctlr->mem_ops = &nxp_xspi_mem_ops;
>
> --
> 2.34.1
>
>