serial: samsung: Avoid waiting forever for TX ready

The no_console_suspend option allows the console to write to the UART
during early resume, before the serial port itself is resumed. Such
writes hang indefinitely waiting for TX ready.

This adds a check to the console putchar function to drop characters
instead of hanging if the port hasn't been initialized. That way, we
can use no_console_suspend without risk of hanging.

Signed-off-by: Michael Spang <spang@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 19 insertions, 3 deletions

diff --git a/drivers/tty/serial/samsung.c b/drivers/tty/serial/samsung.c
index 78d9c55a9f84..7883f11b8c53 100644
--- a/drivers/tty/serial/samsung.c
+++ b/drivers/tty/serial/samsung.c
@@ -1367,6 +1367,13 @@ s3c24xx_serial_console_txrdy(struct uart_port *port, unsigned int ufcon)
         return (utrstat & S3C2410_UTRSTAT_TXE) ? 1 : 0;
 }
 
+static bool
+s3c24xx_port_configured(unsigned int ucon)
+{
+        /* consider the serial port configured if the tx/rx mode set */
+        return (ucon & 0xf) != 0;
+}
+
 #ifdef CONFIG_CONSOLE_POLL
 /*
  * Console polling routines for writing and reading from the uart while
@@ -1389,6 +1396,11 @@ static void s3c24xx_serial_put_poll_char(struct uart_port *port,
                 unsigned char c)
 {
         unsigned int ufcon = rd_regl(cons_uart, S3C2410_UFCON);
+        unsigned int ucon = rd_regl(cons_uart, S3C2410_UCON);
+
+        /* not possible to xmit on unconfigured port */
+        if (!s3c24xx_port_configured(ucon))
+                return;
 
         while (!s3c24xx_serial_console_txrdy(port, ufcon))
                 cpu_relax();
@@ -1401,6 +1413,12 @@ static void
 s3c24xx_serial_console_putchar(struct uart_port *port, int ch)
 {
         unsigned int ufcon = rd_regl(cons_uart, S3C2410_UFCON);
+        unsigned int ucon = rd_regl(cons_uart, S3C2410_UCON);
+
+        /* not possible to xmit on unconfigured port */
+        if (!s3c24xx_port_configured(ucon))
+                return;
+
         while (!s3c24xx_serial_console_txrdy(port, ufcon))
                 barrier();
         wr_regb(cons_uart, S3C2410_UTXH, ch);
@@ -1433,9 +1451,7 @@ s3c24xx_serial_get_options(struct uart_port *port, int *baud,
             "registers: ulcon=%08x, ucon=%08x, ubdriv=%08x\n",
             port, ulcon, ucon, ubrdiv);
 
-        if ((ucon & 0xf) != 0) {
-                /* consider the serial port configured if the tx/rx mode set */
-
+        if (s3c24xx_port_configured(ucon)) {
                 switch (ulcon & S3C2410_LCON_CSMASK) {
                 case S3C2410_LCON_CS5:
                         *bits = 5;