on imx8(mm) the RXDMUXSEL needs to be set for data going over the wire (as observable on a connected 'scope) to actually make it into the RXFIFO
the reference manual is not overly clear about this, and only mentiones that "UCR3_RXDMUXSEL should always be set." - and since the CR3 register reverts to its reset values after setting the baudrate, setting this bit is done during '_mxc_serial_setbgr'
Signed-off-by: Johannes Schneider johannes.schneider@leica-geosystems.com
---
drivers/serial/serial_mxc.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/drivers/serial/serial_mxc.c b/drivers/serial/serial_mxc.c index 70a0e5e919..5f283cc635 100644 --- a/drivers/serial/serial_mxc.c +++ b/drivers/serial/serial_mxc.c @@ -61,6 +61,11 @@ #define UCR3_AWAKEN (1<<4) /* Async wake interrupt enable */ #define UCR3_REF25 (1<<3) /* Ref freq 25 MHz */ #define UCR3_REF30 (1<<2) /* Ref Freq 30 MHz */ + +//imx8 names these bitsfields instead: +#define UCR3_DTRDEN BIT(3) /* bit not used in this chip */ +#define UCR3_RXDMUXSEL BIT(2) /* RXD muxed input selected; 'should always be set' */ + #define UCR3_INVT (1<<1) /* Inverted Infrared transmission */ #define UCR3_BPEN (1<<0) /* Preset registers enable */ #define UCR4_CTSTL_32 (32<<10) /* CTS trigger level (32 chars) */ @@ -176,6 +181,12 @@ static void _mxc_serial_setbrg(struct mxc_uart *base, unsigned long clk,
writel(UCR2_WS | UCR2_IRTS | UCR2_RXEN | UCR2_TXEN | UCR2_SRST, &base->cr2); + + // setting the baudrate triggers a reset, returning cr3 to its + // reset value but UCR3_RXDMUXSEL "should always be set." + // according to the imx8 reference-manual + writel(readl(&base->cr3) | UCR3_RXDMUXSEL, &base->cr3); + writel(UCR1_UARTEN, &base->cr1); }