[PATCH 2/4] spi: spi-fsl-dspi: Use non-coherent memory for DMA

James Clark
2025-06-09T15:33:40Z

Using coherent memory here isn't functionally necessary. Because the
change to use non-coherent memory isn't overly complex and only a few
synchronization points are required, we might as well do it while fixing
up some other DMA issues.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: James Clark <james.clark@linaro.org>
---
drivers/spi/spi-fsl-dspi.c | 55 +++++++++++++++++++++++++++++-----------------
1 file changed, 35 insertions(+), 20 deletions(-)

diff --git a/drivers/spi/spi-fsl-dspi.c b/drivers/spi/spi-fsl-dspi.c
index 386a17871e79..567632042f8f 100644
--- a/drivers/spi/spi-fsl-dspi.c
+++ b/drivers/spi/spi-fsl-dspi.c
@@ -247,6 +247,11 @@ struct fsl_dspi {
void (*dev_to_host)(struct fsl_dspi *dspi, u32 rxdata);
};

+static int dspi_dma_transfer_size(struct fsl_dspi *dspi)
+{
+ return dspi->words_in_flight * DMA_SLAVE_BUSWIDTH_4_BYTES;
+}
+
static void dspi_native_host_to_dev(struct fsl_dspi *dspi, u32 *txdata)
{
switch (dspi->oper_word_size) {
@@ -361,7 +366,10 @@ static void dspi_tx_dma_callback(void *arg)
{
struct fsl_dspi *dspi = arg;
struct fsl_dspi_dma *dma = dspi->dma;
+ struct device *dev = &dspi->pdev->dev;

+ dma_sync_single_for_cpu(dev, dma->tx_dma_phys,
+ dspi_dma_transfer_size(dspi), DMA_TO_DEVICE);
complete(&dma->cmd_tx_complete);
}

@@ -369,9 +377,13 @@ static void dspi_rx_dma_callback(void *arg)
{
struct fsl_dspi *dspi = arg;
struct fsl_dspi_dma *dma = dspi->dma;
+ struct device *dev = &dspi->pdev->dev;
int i;

if (dspi->rx) {
+ dma_sync_single_for_cpu(dev, dma->rx_dma_phys,
+ dspi_dma_transfer_size(dspi),
+ DMA_FROM_DEVICE);
for (i = 0; i < dspi->words_in_flight; i++)
dspi_push_rx(dspi, dspi->dma->rx_dma_buf[i]);
}
@@ -381,6 +393,7 @@ static void dspi_rx_dma_callback(void *arg)

static int dspi_next_xfer_dma_submit(struct fsl_dspi *dspi)
{
+ size_t size = dspi_dma_transfer_size(dspi);
struct device *dev = &dspi->pdev->dev;
struct fsl_dspi_dma *dma = dspi->dma;
int time_left;
@@ -389,10 +402,9 @@ static int dspi_next_xfer_dma_submit(struct fsl_dspi *dspi)
for (i = 0; i < dspi->words_in_flight; i++)
dspi->dma->tx_dma_buf[i] = dspi_pop_tx_pushr(dspi);

+ dma_sync_single_for_device(dev, dma->tx_dma_phys, size, DMA_TO_DEVICE);
dma->tx_desc = dmaengine_prep_slave_single(dma->chan_tx,
- dma->tx_dma_phys,
- dspi->words_in_flight *
- DMA_SLAVE_BUSWIDTH_4_BYTES,
+ dma->tx_dma_phys, size,
DMA_MEM_TO_DEV,
DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
if (!dma->tx_desc) {
@@ -407,10 +419,10 @@ static int dspi_next_xfer_dma_submit(struct fsl_dspi *dspi)
return -EINVAL;
}

+ dma_sync_single_for_device(dev, dma->rx_dma_phys, size,
+ DMA_FROM_DEVICE);
dma->rx_desc = dmaengine_prep_slave_single(dma->chan_rx,
- dma->rx_dma_phys,
- dspi->words_in_flight *
- DMA_SLAVE_BUSWIDTH_4_BYTES,
+ dma->rx_dma_phys, size,
DMA_DEV_TO_MEM,
DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
if (!dma->rx_desc) {
@@ -512,17 +524,17 @@ static int dspi_request_dma(struct fsl_dspi *dspi, phys_addr_t phy_addr)
goto err_tx_channel;
}

- dma->tx_dma_buf = dma_alloc_coherent(dma->chan_tx->device->dev,
- dma_bufsize, &dma->tx_dma_phys,
- GFP_KERNEL);
+ dma->tx_dma_buf = dma_alloc_noncoherent(dma->chan_tx->device->dev,
+ dma_bufsize, &dma->tx_dma_phys,
+ DMA_TO_DEVICE, GFP_KERNEL);
if (!dma->tx_dma_buf) {
ret = -ENOMEM;
goto err_tx_dma_buf;
}

- dma->rx_dma_buf = dma_alloc_coherent(dma->chan_rx->device->dev,
- dma_bufsize, &dma->rx_dma_phys,
- GFP_KERNEL);
+ dma->rx_dma_buf = dma_alloc_noncoherent(dma->chan_rx->device->dev,
+ dma_bufsize, &dma->rx_dma_phys,
+ DMA_FROM_DEVICE, GFP_KERNEL);
if (!dma->rx_dma_buf) {
ret = -ENOMEM;
goto err_rx_dma_buf;
@@ -557,11 +569,12 @@ static int dspi_request_dma(struct fsl_dspi *dspi, phys_addr_t phy_addr)
return 0;

err_slave_config:
- dma_free_coherent(dma->chan_rx->device->dev,
- dma_bufsize, dma->rx_dma_buf, dma->rx_dma_phys);
+ dma_free_noncoherent(dma->chan_rx->device->dev, dma_bufsize,
+ dma->rx_dma_buf, dma->rx_dma_phys,
+ DMA_FROM_DEVICE);
err_rx_dma_buf:
- dma_free_coherent(dma->chan_tx->device->dev,
- dma_bufsize, dma->tx_dma_buf, dma->tx_dma_phys);
+ dma_free_noncoherent(dma->chan_tx->device->dev, dma_bufsize,
+ dma->tx_dma_buf, dma->tx_dma_phys, DMA_TO_DEVICE);
err_tx_dma_buf:
dma_release_channel(dma->chan_tx);
err_tx_channel:
@@ -582,14 +595,16 @@ static void dspi_release_dma(struct fsl_dspi *dspi)
return;

if (dma->chan_tx) {
- dma_free_coherent(dma->chan_tx->device->dev, dma_bufsize,
- dma->tx_dma_buf, dma->tx_dma_phys);
+ dma_free_noncoherent(dma->chan_tx->device->dev, dma_bufsize,
+ dma->tx_dma_buf, dma->tx_dma_phys,
+ DMA_TO_DEVICE);
dma_release_channel(dma->chan_tx);
}

if (dma->chan_rx) {
- dma_free_coherent(dma->chan_rx->device->dev, dma_bufsize,
- dma->rx_dma_buf, dma->rx_dma_phys);
+ dma_free_noncoherent(dma->chan_rx->device->dev, dma_bufsize,
+ dma->rx_dma_buf, dma->rx_dma_phys,
+ DMA_FROM_DEVICE);
dma_release_channel(dma->chan_rx);
}
}

--
2.34.1