tty: xuartps: Force enable the UART in xuartps_console_write

It is possible that under certain circumstances xuartps_console_write is entered
while the UART disabled. When this happens the code will busy loop in
xuartps_console_putchar, since the character is never written and the TXEMPTY
flag is never set. The result is a system lockup. This patch force enables the
UART for the duration of xuartps_console_write to avoid this.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: John Linn <john.linn@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
index 6e8ec6e9d5a2ef7de8a8d7870dfa8fbcd34d5270..fdc739b55eb33998d2297f43692debbfca375bdd 100644 (file)
--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -953,7 +953,7 @@ static void xuartps_console_write(struct console *co, const char *s,
 {
        struct uart_port *port = &xuartps_port[co->index];
        unsigned long flags;
-       unsigned int imr;
+       unsigned int imr, ctrl;
        int locked = 1;
 
        if (oops_in_progress)
@@ -965,9 +965,19 @@ static void xuartps_console_write(struct console *co, const char *s,
        imr = xuartps_readl(XUARTPS_IMR_OFFSET);
        xuartps_writel(imr, XUARTPS_IDR_OFFSET);
 
+       /*
+        * Make sure that the tx part is enabled. Set the TX enable bit and
+        * clear the TX disable bit to enable the transmitter.
+        */
+       ctrl = xuartps_readl(XUARTPS_CR_OFFSET);
+       xuartps_writel((ctrl & ~XUARTPS_CR_TX_DIS) | XUARTPS_CR_TX_EN,
+               XUARTPS_CR_OFFSET);
+
        uart_console_write(port, s, count, xuartps_console_putchar);
        xuartps_console_wait_tx(port);
 
+       xuartps_writel(ctrl, XUARTPS_CR_OFFSET);
+
        /* restore interrupt state, it seems like there may be a h/w bug
         * in that the interrupt enable register should not need to be
         * written based on the data sheet