serial: 8250: Add NOMSI bug for bcm2835aux

The BCM2835 mini-UART has no modem status interrupt, causing all
transmission to stop, never to use, if a speed change ever happens
while the CTS signal is high.

Add a simple polling mechanism in order to allow recovery in that
situation.

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

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index 1aa3e55..ae5b995 100644 (file)
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -92,6 +92,7 @@ struct serial8250_config {
 #define UART_BUG_NOMSR BIT(2)  /* UART has buggy MSR status bits (Au1x00) */
 #define UART_BUG_THRE  BIT(3)  /* UART has buggy THRE reassertion */
 #define UART_BUG_TXRACE        BIT(5)  /* UART Tx fails to set remote DR */
+#define UART_BUG_NOMSI BIT(6)  /* UART has no modem status interrupt */
 
 
 #ifdef CONFIG_SERIAL_8250_SHARE_IRQ

diff --git a/drivers/tty/serial/8250/8250_bcm2835aux.c b/drivers/tty/serial/8250/8250_bcm2835aux.c
index 01df594..f31e3c9 100644 (file)
--- a/drivers/tty/serial/8250/8250_bcm2835aux.c
+++ b/drivers/tty/serial/8250/8250_bcm2835aux.c
@@ -109,6 +109,7 @@ static int bcm2835aux_serial_probe(struct platform_device *pdev)
                        UPF_SKIP_TEST | UPF_IOREMAP;
        up.port.rs485_config = serial8250_em485_config;
        up.port.rs485_supported = serial8250_em485_supported;
+       up.bugs |= UART_BUG_NOMSI;
        up.rs485_start_tx = bcm2835aux_rs485_start_tx;
        up.rs485_stop_tx = bcm2835aux_rs485_stop_tx;
 

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 3449f87..e561f21 100644 (file)
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -253,6 +253,18 @@ static void serial8250_timeout(struct timer_list *t)
        mod_timer(&up->timer, jiffies + uart_poll_timeout(&up->port));
 }
 
+static void serial8250_cts_poll_timeout(struct timer_list *t)
+{
+       struct uart_8250_port *up = from_timer(up, t, timer);
+       unsigned long flags;
+
+       spin_lock_irqsave(&up->port.lock, flags);
+       serial8250_modem_status(up);
+       spin_unlock_irqrestore(&up->port.lock, flags);
+       if (up->port.hw_stopped)
+               mod_timer(&up->timer, jiffies + 1);
+}
+
 static void serial8250_backup_timeout(struct timer_list *t)
 {
        struct uart_8250_port *up = from_timer(up, t, timer);
@@ -315,6 +327,9 @@ static void univ8250_setup_timer(struct uart_8250_port *up)
                          uart_poll_timeout(port) + HZ / 5);
        }
 
+       if (up->bugs & UART_BUG_NOMSI)
+               up->timer.function = serial8250_cts_poll_timeout;
+
        /*
         * If the "interrupt" for this port doesn't correspond with any
         * hardware interrupt, we use a timer-based system.  The original

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 1416273..345076d 100644 (file)
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1535,6 +1535,9 @@ static void serial8250_stop_tx(struct uart_port *port)
                serial_icr_write(up, UART_ACR, up->acr);
        }
        serial8250_rpm_put(up);
+
+       if (port->hw_stopped && (up->bugs & UART_BUG_NOMSI))
+               mod_timer(&up->timer, jiffies + 1);
 }
 
 static inline void __start_tx(struct uart_port *port)
@@ -1648,6 +1651,9 @@ static void serial8250_start_tx(struct uart_port *port)
        /* Port locked to synchronize UART_IER access against the console. */
        lockdep_assert_held_once(&port->lock);
 
+       if (up->bugs & UART_BUG_NOMSI)
+               del_timer(&up->timer);
+
        if (!port->x_char && uart_circ_empty(&port->state->xmit))
                return;
 
@@ -1872,6 +1878,9 @@ unsigned int serial8250_modem_status(struct uart_8250_port *up)
                        uart_handle_cts_change(port, status & UART_MSR_CTS);
 
                wake_up_interruptible(&port->state->port.delta_msr_wait);
+       } else if (up->bugs & UART_BUG_NOMSI && port->hw_stopped &&
+                  status & UART_MSR_CTS) {
+               uart_handle_cts_change(port, status & UART_MSR_CTS);
        }
 
        return status;