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>

2 files changed, 5 insertions, 5 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);
 }
diff --git a/drivers/serial/amba-pl011.c b/drivers/serial/amba-pl011.c
index 743ebf5f16da..eb4cb480b93e 100644
--- a/drivers/serial/amba-pl011.c
+++ b/drivers/serial/amba-pl011.c
@@ -342,9 +342,9 @@ static int pl010_get_poll_char(struct uart_port *port)
         struct uart_amba_port *uap = (struct uart_amba_port *)port;
         unsigned int status;
 
-        do {
-                status = readw(uap->port.membase + UART01x_FR);
-        } while (status & UART01x_FR_RXFE);
+        status = readw(uap->port.membase + UART01x_FR);
+        if (status & UART01x_FR_RXFE)
+                return NO_POLL_CHAR;
 
         return readw(uap->port.membase + UART01x_DR);
 }