i.MX: Support serial RS-232 break properly

Linux does not detect a break from this IMX serial driver as a magic
sysrq.  Nor does it note a break in the port error counts.

The former is because the Linux driver uses the BRCD bit in the USR2
register to trigger the RS-232 break handler in the kernel, which is
where sysrq hooks in.  The emulated UART was not setting this status
bit.

The latter is because the Linux driver expects, in addition to the BRK
bit, that the ERR bit is set when a break is read in the FIFO.  A break
should also count as a frame error, so add that bit too.

Cc: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Trent Piepho <tpiepho@impinj.com>
Message-id: 20180320013657.25038-1-tpiepho@impinj.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/char/imx_serial.c

@@ -308,6 +308,9 @@ static void imx_put_data(void *opaque, uint32_t value)
     s->usr2 |= USR2_RDR;
     s->uts1 &= ~UTS1_RXEMPTY;
     s->readbuff = value;
+    if (value & URXD_BRK) {
+        s->usr2 |= USR2_BRCD;
+    }
     imx_update(s);
 }
 
@@ -319,7 +322,7 @@ static void imx_receive(void *opaque, const uint8_t *buf, int size)
 static void imx_event(void *opaque, int event)
 {
     if (event == CHR_EVENT_BREAK) {
-        imx_put_data(opaque, URXD_BRK);
+        imx_put_data(opaque, URXD_BRK | URXD_FRMERR | URXD_ERR);
     }
 }
 

include/hw/char/imx_serial.h

@@ -26,6 +26,7 @@
 
 #define URXD_CHARRDY    (1<<15)   /* character read is valid */
 #define URXD_ERR        (1<<14)   /* Character has error */
+#define URXD_FRMERR     (1<<12)   /* Character has frame error */
 #define URXD_BRK        (1<<11)   /* Break received */
 
 #define USR1_PARTYER    (1<<15)   /* Parity Error */