From fab44ef1adcc585440c07c90539e2b9e2cded4bf Mon Sep 17 00:00:00 2001 From: Anton Bondarenko Date: Sat, 5 Dec 2015 17:57:00 +0100 Subject: [PATCH] spi: imx: reorder HW operations enable order to avoid possible RX data loss The overflow may happen due to rescheduling for another task and/or interrupt if we enable SPI HW before starting RX DMA. So RX DMA enabled first to make sure data would be read out from FIFO ASAP. TX DMA enabled next to start filling TX FIFO with new data. And finaly SPI HW enabled to start actual data transfer. The risk rise in case of heavy system load and high SPI clock. Signed-off-by: Anton Bondarenko Signed-off-by: Mark Brown --- drivers/spi/spi-imx.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c index d6dc66542811..e6b1c74ade6b 100644 --- a/drivers/spi/spi-imx.c +++ b/drivers/spi/spi-imx.c @@ -956,10 +956,18 @@ static int spi_imx_dma_transfer(struct spi_imx_data *spi_imx, if (left) writel(dma | (left << MX51_ECSPI_DMA_RXT_WML_OFFSET), spi_imx->base + MX51_ECSPI_DMA); + /* + * Set these order to avoid potential RX overflow. The overflow may + * happen if we enable SPI HW before starting RX DMA due to rescheduling + * for another task and/or interrupt. + * So RX DMA enabled first to make sure data would be read out from FIFO + * ASAP. TX DMA enabled next to start filling TX FIFO with new data. + * And finaly SPI HW enabled to start actual data transfer. + */ + dma_async_issue_pending(master->dma_rx); + dma_async_issue_pending(master->dma_tx); spi_imx->devtype_data->trigger(spi_imx); - dma_async_issue_pending(master->dma_tx); - dma_async_issue_pending(master->dma_rx); /* Wait SDMA to finish the data transfer.*/ timeout = wait_for_completion_timeout(&spi_imx->dma_tx_completion, IMX_DMA_TIMEOUT);