spi/imx: select master mode for all channels

The hardware seems to have a race condition when the inactive
channels are in slave mode. We support master mode only, so
we can just switch all channels to master mode.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
[ukleinek: add more verbose comment about the race]
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

1 files changed, 9 insertions, 3 deletions

diff --git a/drivers/spi/spi_imx.c b/drivers/spi/spi_imx.c
index 1cf9d5faabf4..69d6dba67c19 100644
--- a/drivers/spi/spi_imx.c
+++ b/drivers/spi/spi_imx.c
@@ -174,7 +174,7 @@ static unsigned int spi_imx_clkdiv_2(unsigned int fin,
 #define SPI_IMX2_3_CTRL         0x08
 #define SPI_IMX2_3_CTRL_ENABLE          (1 <<  0)
 #define SPI_IMX2_3_CTRL_XCH             (1 <<  2)
-#define SPI_IMX2_3_CTRL_MODE(cs)        (1 << ((cs) +  4))
+#define SPI_IMX2_3_CTRL_MODE_MASK       (0xf << 4)
 #define SPI_IMX2_3_CTRL_POSTDIV_OFFSET  8
 #define SPI_IMX2_3_CTRL_PREDIV_OFFSET   12
 #define SPI_IMX2_3_CTRL_CS(cs)          ((cs) << 18)
@@ -253,8 +253,14 @@ static int __maybe_unused spi_imx2_3_config(struct spi_imx_data *spi_imx,
 {
         u32 ctrl = SPI_IMX2_3_CTRL_ENABLE, cfg = 0;
 
-        /* set master mode */
-        ctrl |= SPI_IMX2_3_CTRL_MODE(config->cs);
+        /*
+         * The hardware seems to have a race condition when changing modes. The
+         * current assumption is that the selection of the channel arrives
+         * earlier in the hardware than the mode bits when they are written at
+         * the same time.
+         * So set master mode for all channels as we do not support slave mode.
+         */
+        ctrl |= SPI_IMX2_3_CTRL_MODE_MASK;
 
         /* set clock speed */
         ctrl |= spi_imx2_3_clkdiv(spi_imx->spi_clk, config->speed_hz);