From: Russell King <rmk@dyn-67.arm.linux.org.uk>
Date: Thu, 23 Jun 2005 14:05:41 +0000 (+0100)
Subject: [PATCH] Serial: Mobility's 16550A ports need a helping hand
X-Git-Tag: v2.6.13-rc1~68^2~384^2~1
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=55d3b282b90620e02e825304a9433732a84c58a5;p=linux-2.6

[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 27cc288e91..341c644591 100644
--- 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 cd5c3dd2d9..9225c82fae 100644
--- 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