tty: amba-pl011: Add un/throttle support

The PL011 driver lacks throttle and unthrottle methods. As a result,
sending more data to the Pi than it can immediately sink while CRTSCTS
is enabled causes a NULL pointer to be followed.

Add a throttle handler that disables the RX interrupts, and an
unthrottle handler that reenables them.

Signed-off-by: Phil Elwell <phil@raspberrypi.org>

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 8b1f816..9df9bc8 100644 (file)
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1317,6 +1317,32 @@ static void pl011_start_tx(struct uart_port *port)
                pl011_start_tx_pio(uap);
 }
 
+static void pl011_throttle(struct uart_port *port)
+{
+       struct uart_amba_port *uap =
+           container_of(port, struct uart_amba_port, port);
+       unsigned long flags;
+
+       spin_lock_irqsave(&uap->port.lock, flags);
+       uap->im &= ~(UART011_RTIM | UART011_RXIM);
+       pl011_write(uap->im, uap, REG_IMSC);
+       spin_unlock_irqrestore(&uap->port.lock, flags);
+}
+
+static void pl011_unthrottle(struct uart_port *port)
+{
+       struct uart_amba_port *uap =
+           container_of(port, struct uart_amba_port, port);
+       unsigned long flags;
+
+       spin_lock_irqsave(&uap->port.lock, flags);
+       uap->im |= UART011_RTIM;
+       if (!pl011_dma_rx_running(uap))
+           uap->im |= UART011_RXIM;
+       pl011_write(uap->im, uap, REG_IMSC);
+       spin_unlock_irqrestore(&uap->port.lock, flags);
+}
+
 static void pl011_stop_rx(struct uart_port *port)
 {
        struct uart_amba_port *uap =
@@ -2156,6 +2182,8 @@ static const struct uart_ops amba_pl011_pops = {
        .stop_tx        = pl011_stop_tx,
        .start_tx       = pl011_start_tx,
        .stop_rx        = pl011_stop_rx,
+       .throttle       = pl011_throttle,
+       .unthrottle     = pl011_unthrottle,
        .enable_ms      = pl011_enable_ms,
        .break_ctl      = pl011_break_ctl,
        .startup        = pl011_startup,