diff options
Diffstat (limited to 'drivers/spi/spi-dw-dma.c')
| -rw-r--r-- | drivers/spi/spi-dw-dma.c | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/drivers/spi/spi-dw-dma.c b/drivers/spi/spi-dw-dma.c index 5986c520b196..bb390ff67d1d 100644 --- a/drivers/spi/spi-dw-dma.c +++ b/drivers/spi/spi-dw-dma.c @@ -372,8 +372,20 @@ static int dw_spi_dma_setup(struct dw_spi *dws, struct spi_transfer *xfer) { u16 imr = 0, dma_ctrl = 0; + /* + * Having a Rx DMA channel serviced with higher priority than a Tx DMA + * channel might not be enough to provide a well balanced DMA-based + * SPI transfer interface. There might still be moments when the Tx DMA + * channel is occasionally handled faster than the Rx DMA channel. + * That in its turn will eventually cause the SPI Rx FIFO overflow if + * SPI bus speed is high enough to fill the SPI Rx FIFO in before it's + * cleared by the Rx DMA channel. In order to fix the problem the Tx + * DMA activity is intentionally slowed down by limiting the SPI Tx + * FIFO depth with a value twice bigger than the Tx burst length + * calculated earlier by the dw_spi_dma_maxburst_init() method. + */ dw_writel(dws, DW_SPI_DMARDLR, dws->rxburst - 1); - dw_writel(dws, DW_SPI_DMATDLR, dws->fifo_len - dws->txburst); + dw_writel(dws, DW_SPI_DMATDLR, dws->txburst); if (xfer->tx_buf) dma_ctrl |= SPI_DMA_TDMAE; |