[PATCH] SPI: drain MXC SPI transfer buffer when probing device

[daniel@caiaq.de (Daniel Mack)]

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>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Uwe Kleine-K?nig <u.kleine-koenig@pengutronix.de>
Cc: spi-devel-general at lists.sourceforge.net
---
 drivers/spi/spi_imx.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/drivers/spi/spi_imx.c b/drivers/spi/spi_imx.c
index 89c22ef..1b17f44 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);
-- 
1.6.5.2