spi/i.mx: drain MXC SPI transfer buffer when probing device

On the MX31litekit, the bootloader seems to communicate with the MC13783
PMIC chip before booting Linux. However, it does not flush all the
buffers properly after that, which makes the imx-spi driver read
bogus data when probing the MC13783.

Fix that by draining the SPI receive buffer on startup.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

1 files changed, 8 insertions, 0 deletions

diff --git a/drivers/spi/spi_imx.c b/drivers/spi/spi_imx.c
index 89c22efedfb0..1b17f443dee7 100644
--- a/drivers/spi/spi_imx.c
+++ b/drivers/spi/spi_imx.c
@@ -44,6 +44,9 @@
 #define MXC_CSPIINT             0x0c
 #define MXC_RESET               0x1c
 
+#define MX3_CSPISTAT            0x14
+#define MX3_CSPISTAT_RR         (1 << 3)
+
 /* generic defines to abstract from the different register layouts */
 #define MXC_INT_RR      (1 << 0) /* Receive data ready interrupt */
 #define MXC_INT_TE      (1 << 1) /* Transmit FIFO empty interrupt */
@@ -593,6 +596,11 @@ static int __init spi_imx_probe(struct platform_device *pdev)
         if (!cpu_is_mx31() || !cpu_is_mx35())
                 writel(1, spi_imx->base + MXC_RESET);
 
+        /* drain receive buffer */
+        if (cpu_is_mx31() || cpu_is_mx35())
+                while (readl(spi_imx->base + MX3_CSPISTAT) & MX3_CSPISTAT_RR)
+                        readl(spi_imx->base + MXC_CSPIRXDATA);
+
         spi_imx->intctrl(spi_imx, 0);
 
         ret = spi_bitbang_start(&spi_imx->bitbang);