1 files changed, 29 insertions, 0 deletions

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index ea7aa973ab43..d7e1edec50b5 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1284,11 +1284,40 @@ static void pl011_break_ctl(struct uart_port *port, int break_state)
 }
 
 #ifdef CONFIG_CONSOLE_POLL
+
+static void pl011_quiesce_irqs(struct uart_port *port)
+{
+        struct uart_amba_port *uap = (struct uart_amba_port *)port;
+        unsigned char __iomem *regs = uap->port.membase;
+
+        writew(readw(regs + UART011_MIS), regs + UART011_ICR);
+        /*
+         * There is no way to clear TXIM as this is "ready to transmit IRQ", so
+         * we simply mask it. start_tx() will unmask it.
+         *
+         * Note we can race with start_tx(), and if the race happens, the
+         * polling user might get another interrupt just after we clear it.
+         * But it should be OK and can happen even w/o the race, e.g.
+         * controller immediately got some new data and raised the IRQ.
+         *
+         * And whoever uses polling routines assumes that it manages the device
+         * (including tx queue), so we're also fine with start_tx()'s caller
+         * side.
+         */
+        writew(readw(regs + UART011_IMSC) & ~UART011_TXIM, regs + UART011_IMSC);
+}
+
 static int pl011_get_poll_char(struct uart_port *port)
 {
         struct uart_amba_port *uap = (struct uart_amba_port *)port;
         unsigned int status;
 
+        /*
+         * The caller might need IRQs lowered, e.g. if used with KDB NMI
+         * debugger.
+         */
+        pl011_quiesce_irqs(port);
+
         status = readw(uap->port.membase + UART01x_FR);
         if (status & UART01x_FR_RXFE)
                 return NO_POLL_CHAR;