kgdb,8250,pl011: Return immediately from console poll

The design of the kdb shell requires that every device that can
provide input to kdb have a polling routine that exits immediately if
there is no character available.  This is required in order to get the
page scrolling mechanism working.

Changing the kernel debugger I/O API to require all polling character
routines to exit immediately if there is no data allows the kernel
debugger to process multiple input channels.

NO_POLL_CHAR will be the return code to the polling routine when ever
there is no character available.

CC: linux-serial@vger.kernel.org
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index 2b1ea3d4c4f4..891e1dd65f24 100644
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -1891,8 +1891,8 @@ static int serial8250_get_poll_char(struct uart_port *port)
         struct uart_8250_port *up = (struct uart_8250_port *)port;
         unsigned char lsr = serial_inp(up, UART_LSR);
 
-        while (!(lsr & UART_LSR_DR))
-                lsr = serial_inp(up, UART_LSR);
+        if (!(lsr & UART_LSR_DR))
+                return NO_POLL_CHAR;
 
         return serial_inp(up, UART_RX);
 }