[PATCH] Serial: Mobility's 16550A ports need a helping hand

The Mobility 16550A serial ports don't behave the same as standard
16550A ports, and need a helping hand to get them going once the
transmitter has drained and been disabled.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index 27cc288e91d0465b1d9de49ca13678b8643791d7..341c644591ae4a95a9dfef2ed7c2abee8c7beef2 100644 (file)
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -1027,6 +1027,8 @@ static void serial8250_stop_tx(struct uart_port *port, unsigned int tty_stop)
        }
 }
 
+static void transmit_chars(struct uart_8250_port *up);
+
 static void serial8250_start_tx(struct uart_port *port, unsigned int tty_start)
 {
        struct uart_8250_port *up = (struct uart_8250_port *)port;
@@ -1034,6 +1036,14 @@ static void serial8250_start_tx(struct uart_port *port, unsigned int tty_start)
        if (!(up->ier & UART_IER_THRI)) {
                up->ier |= UART_IER_THRI;
                serial_out(up, UART_IER, up->ier);
+
+               if (up->capabilities & UART_BUG_TXEN) {
+                       unsigned char lsr, iir;
+                       lsr = serial_in(up, UART_LSR);
+                       iir = serial_in(up, UART_IIR);
+                       if (lsr & UART_LSR_TEMT && iir & UART_IIR_NO_INT)
+                               transmit_chars(up);
+               }
        }
        /*
         * We only do this from uart_start
@@ -1439,6 +1449,7 @@ static int serial8250_startup(struct uart_port *port)
 {
        struct uart_8250_port *up = (struct uart_8250_port *)port;
        unsigned long flags;
+       unsigned char lsr, iir;
        int retval;
 
        up->capabilities = uart_config[up->port.type].flags;
@@ -1542,6 +1553,26 @@ static int serial8250_startup(struct uart_port *port)
                        up->port.mctrl |= TIOCM_OUT2;
 
        serial8250_set_mctrl(&up->port, up->port.mctrl);
+
+       /*
+        * Do a quick test to see if we receive an
+        * interrupt when we enable the TX irq.
+        */
+       serial_outp(up, UART_IER, UART_IER_THRI);
+       lsr = serial_in(up, UART_LSR);
+       iir = serial_in(up, UART_IIR);
+       serial_outp(up, UART_IER, 0);
+
+       if (lsr & UART_LSR_TEMT && iir & UART_IIR_NO_INT) {
+               if (!(up->capabilities & UART_BUG_TXEN)) {
+                       up->capabilities |= UART_BUG_TXEN;
+                       pr_debug("ttyS%d - enabling bad tx status workarounds\n",
+                                port->line);
+               }
+       } else {
+               up->capabilities &= ~UART_BUG_TXEN;
+       }
+
        spin_unlock_irqrestore(&up->port.lock, flags);
 
        /*

diff --git a/drivers/serial/8250.h b/drivers/serial/8250.h
index cd5c3dd2d9106512efc5ef6dc3318734aa44cfa2..9225c82faeb8e13b7b88b8a7b5e81a409c72aca3 100644 (file)
--- a/drivers/serial/8250.h
+++ b/drivers/serial/8250.h
@@ -52,6 +52,7 @@ struct serial8250_config {
 #define UART_CAP_UUE   (1 << 12)       /* UART needs IER bit 6 set (Xscale) */
 
 #define UART_BUG_QUOT  (1 << 0)        /* UART has buggy quot LSB */
+#define UART_BUG_TXEN  (1 << 1)        /* UART has buggy TX IIR status */
 
 #if defined(__i386__) && (defined(CONFIG_M386) || defined(CONFIG_M486))
 #define _INLINE_ inline