From 0a9c8998e75b69b3c347751a65ddd5bf7e72b2dd Mon Sep 17 00:00:00 2001 From: Trent Piepho Date: Mon, 4 Mar 2019 23:02:36 +0000 Subject: spi: imx: add module parameter to control DMA use Add the boolean module parameter "use_dma" to control the use of DMA by the driver. There are about two dozen other drivers with a "use_dma" parameter of some sort. DMA may allow faster and more efficient transfers than using PIO, but it also adds overhead for small transfers. High speed receive operations may be less likely to have issues with FIFO overflow when using DMA than when using PIO. The eCSPI appears to insert a 4 bit pause after each word in DMA mode, not done in PIO mode, which can make DMA transfers 50% slower than PIO. In some cases DMA may be a net win while in others PIO might be. It depends on the application. So allow DMA to be enabled or disabled at the driver level. The default will be to have it enabled when possible. Signed-off-by: Trent Piepho Signed-off-by: Mark Brown --- drivers/spi/spi-imx.c | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'drivers/spi/spi-imx.c') diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c index 6ec647bbba77..e08646e715ba 100644 --- a/drivers/spi/spi-imx.c +++ b/drivers/spi/spi-imx.c @@ -28,6 +28,10 @@ #define DRIVER_NAME "spi_imx" +static bool use_dma = true; +module_param(use_dma, bool, 0644); +MODULE_PARM_DESC(use_dma, "Enable usage of DMA when available (default)"); + #define MXC_CSPIRXDATA 0x00 #define MXC_CSPITXDATA 0x04 #define MXC_CSPICTRL 0x08 @@ -219,6 +223,9 @@ static bool spi_imx_can_dma(struct spi_master *master, struct spi_device *spi, { struct spi_imx_data *spi_imx = spi_master_get_devdata(master); + if (!use_dma) + return false; + if (!master->dma_rx) return false; -- cgit v1.2.3-55-g7522 From c842749ea1d32513f9e603c074d60d7aa07cb2ef Mon Sep 17 00:00:00 2001 From: Trent Piepho Date: Mon, 4 Mar 2019 20:18:49 +0000 Subject: spi: imx: stop buffer overflow in RX FIFO flush Commit 71abd29057cb ("spi: imx: Add support for SPI Slave mode") added an RX FIFO flush before start of a transfer. In slave mode, the master may have sent more data than expected and this data will still be in the RX FIFO at the start of the next transfer, and so needs to be flushed. However, the code to do the flush was accidentally saving this data into the previous transfer's RX buffer, clobbering the contents of whatever followed that buffer. Change it to empty the FIFO and throw away the data. Every one of the RX functions for the different eCSPI versions and modes reads the RX FIFO data using the same readl() call, so just use that, rather than using the spi_imx->rx function pointer and making sure all the different rx functions have a working "throw away" mode. There is another issue, which affects master mode when switching from DMA to PIO. There can be extra data in the RX FIFO which triggers this flush code, causing memory corruption in the same manner. I don't know why this data is unexpectedly in the FIFO. It's likely there is a different bug or erratum responsible for that. But regardless of that, I think this is proper fix the for bug at hand here. Fixes: 71abd29057cb ("spi: imx: Add support for SPI Slave mode") Cc: Jiada Wang Cc: Fabio Estevam Cc: Stefan Agner Cc: Shawn Guo Signed-off-by: Trent Piepho Signed-off-by: Mark Brown --- drivers/spi/spi-imx.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/spi/spi-imx.c') diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c index 6ec647bbba77..a81ae29aa68a 100644 --- a/drivers/spi/spi-imx.c +++ b/drivers/spi/spi-imx.c @@ -1494,7 +1494,7 @@ static int spi_imx_transfer(struct spi_device *spi, /* flush rxfifo before transfer */ while (spi_imx->devtype_data->rx_available(spi_imx)) - spi_imx->rx(spi_imx); + readl(spi_imx->base + MXC_CSPIRXDATA); if (spi_imx->slave_mode) return spi_imx_pio_transfer_slave(spi, transfer); -- cgit v1.2.3-55-g7522