consoles: polling support, kgdboc

polled console handling support, to access a console in an irq-less
way while in debug or irq context.

absolutely zero impact as long as CONFIG_CONSOLE_POLL is disabled.
(which is the default)

[ jan.kiszka@siemens.com: lots of cleanups ]
[ mingo@elte.hu: redesign, splitups, cleanups. ]

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Jan Kiszka <jan.kiszka@web.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 58 insertions, 0 deletions

diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index 77f7a7f0646..96a585e1cee 100644
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -1740,6 +1740,60 @@ static inline void wait_for_xmitr(struct uart_8250_port *up, int bits)
         }
 }
 
+#ifdef CONFIG_CONSOLE_POLL
+/*
+ * Console polling routines for writing and reading from the uart while
+ * in an interrupt or debug context.
+ */
+
+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);
+
+        return serial_inp(up, UART_RX);
+}
+
+
+static void serial8250_put_poll_char(struct uart_port *port,
+                         unsigned char c)
+{
+        unsigned int ier;
+        struct uart_8250_port *up = (struct uart_8250_port *)port;
+
+        /*
+         *      First save the IER then disable the interrupts
+         */
+        ier = serial_in(up, UART_IER);
+        if (up->capabilities & UART_CAP_UUE)
+                serial_out(up, UART_IER, UART_IER_UUE);
+        else
+                serial_out(up, UART_IER, 0);
+
+        wait_for_xmitr(up, BOTH_EMPTY);
+        /*
+         *      Send the character out.
+         *      If a LF, also do CR...
+         */
+        serial_out(up, UART_TX, c);
+        if (c == 10) {
+                wait_for_xmitr(up, BOTH_EMPTY);
+                serial_out(up, UART_TX, 13);
+        }
+
+        /*
+         *      Finally, wait for transmitter to become empty
+         *      and restore the IER
+         */
+        wait_for_xmitr(up, BOTH_EMPTY);
+        serial_out(up, UART_IER, ier);
+}
+
+#endif /* CONFIG_CONSOLE_POLL */
+
 static int serial8250_startup(struct uart_port *port)
 {
         struct uart_8250_port *up = (struct uart_8250_port *)port;
@@ -2386,6 +2440,10 @@ static struct uart_ops serial8250_pops = {
         .request_port   = serial8250_request_port,
         .config_port    = serial8250_config_port,
         .verify_port    = serial8250_verify_port,
+#ifdef CONFIG_CONSOLE_POLL
+        .poll_get_char = serial8250_get_poll_char,
+        .poll_put_char = serial8250_put_poll_char,
+#endif
 };
 
 static struct uart_8250_port serial8250_ports[UART_NR];