pmac_zilog: Fix unexpected irq

On most 68k Macs the SCC IRQ is an autovector interrupt and cannot be
masked. This can be a problem when pmac_zilog starts up.

For example, the serial debugging code in arch/m68k/kernel/head.S may be
used beforehand. It disables the SCC interrupts at the chip but doesn't
ack them. Then when a pmac_zilog port is used, the machine locks up with
"unexpected interrupt".

This can happen in pmz_shutdown() since the irq is freed before the
channel interrupts are disabled.

Fix this by clearing interrupt enable bits before the handler is
uninstalled. Also move the interrupt control bit flipping into a separate
pmz_interrupt_control() routine. Replace all instances of these operations
with calls to this routine. Omit the zssync() calls that seem to serve no
purpose.
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

drivers/tty/serial/pmac_zilog.c

@@ -216,6 +216,18 @@ static void pmz_maybe_update_regs(struct uart_pmac_port *uap)
 	}
 }
 
+static void pmz_interrupt_control(struct uart_pmac_port *uap, int enable)
+{
+	if (enable) {
+		uap->curregs[1] |= INT_ALL_Rx | TxINT_ENAB;
+		if (!ZS_IS_EXTCLK(uap))
+			uap->curregs[1] |= EXT_INT_ENAB;
+	} else {
+		uap->curregs[1] &= ~(EXT_INT_ENAB | TxINT_ENAB | RxINT_MASK);
+	}
+	write_zsreg(uap, R1, uap->curregs[1]);
+}
+
 static struct tty_struct *pmz_receive_chars(struct uart_pmac_port *uap)
 {
 	struct tty_struct *tty = NULL;
@@ -339,9 +351,7 @@ static struct tty_struct *pmz_receive_chars(struct uart_pmac_port *uap)
 
 	return tty;
  flood:
-	uap->curregs[R1] &= ~(EXT_INT_ENAB | TxINT_ENAB | RxINT_MASK);
-	write_zsreg(uap, R1, uap->curregs[R1]);
-	zssync(uap);
+	pmz_interrupt_control(uap, 0);
 	pmz_error("pmz: rx irq flood !\n");
 	return tty;
 }
@@ -990,12 +1000,9 @@ static int pmz_startup(struct uart_port *port)
 	if (ZS_IS_IRDA(uap))
 		pmz_irda_reset(uap);
 
-	/* Enable interrupts emission from the chip */
+	/* Enable interrupt requests for the channel */
 	spin_lock_irqsave(&port->lock, flags);
-	uap->curregs[R1] |= INT_ALL_Rx | TxINT_ENAB;
-	if (!ZS_IS_EXTCLK(uap))
-		uap->curregs[R1] |= EXT_INT_ENAB;
-	write_zsreg(uap, R1, uap->curregs[R1]);
+	pmz_interrupt_control(uap, 1);
 	spin_unlock_irqrestore(&port->lock, flags);
 
 	pmz_debug("pmz: startup() done.\n");
@@ -1015,39 +1022,37 @@ static void pmz_shutdown(struct uart_port *port)
 
 	mutex_lock(&pmz_irq_mutex);
 
-	/* Release interrupt handler */
-	free_irq(uap->port.irq, uap);
-
 	spin_lock_irqsave(&port->lock, flags);
 
-	uap->flags &= ~PMACZILOG_FLAG_IS_OPEN;
-
-	if (!ZS_IS_OPEN(uap->mate))
-		pmz_get_port_A(uap)->flags &= ~PMACZILOG_FLAG_IS_IRQ_ON;
-
-	/* Disable interrupts */
 	if (!ZS_IS_ASLEEP(uap)) {
-		uap->curregs[R1] &= ~(EXT_INT_ENAB | TxINT_ENAB | RxINT_MASK);
-		write_zsreg(uap, R1, uap->curregs[R1]);
-		zssync(uap);
-	}
-
-	if (ZS_IS_CONS(uap) || ZS_IS_ASLEEP(uap)) {
-		spin_unlock_irqrestore(&port->lock, flags);
-		mutex_unlock(&pmz_irq_mutex);
-		return;
-	}
+		/* Disable interrupt requests for the channel */
+		pmz_interrupt_control(uap, 0);
 
-	/* Disable receiver and transmitter.  */
+		if (!ZS_IS_CONS(uap)) {
+			/* Disable receiver and transmitter */
 			uap->curregs[R3] &= ~RxENABLE;
 			uap->curregs[R5] &= ~TxENABLE;
 
-	/* Disable all interrupts and BRK assertion.  */
+			/* Disable break assertion */
 			uap->curregs[R5] &= ~SND_BRK;
 			pmz_maybe_update_regs(uap);
+		}
+	}
 
-	/* Shut the chip down */
-	pmz_set_scc_power(uap, 0);
+	spin_unlock_irqrestore(&port->lock, flags);
+
+	/* Release interrupt handler */
+	free_irq(uap->port.irq, uap);
+
+	spin_lock_irqsave(&port->lock, flags);
+
+	uap->flags &= ~PMACZILOG_FLAG_IS_OPEN;
+
+	if (!ZS_IS_OPEN(uap->mate))
+		pmz_get_port_A(uap)->flags &= ~PMACZILOG_FLAG_IS_IRQ_ON;
+
+	if (!ZS_IS_ASLEEP(uap) && !ZS_IS_CONS(uap))
+		pmz_set_scc_power(uap, 0);	/* Shut the chip down */
 
 	spin_unlock_irqrestore(&port->lock, flags);
 
@@ -1352,19 +1357,15 @@ static void pmz_set_termios(struct uart_port *port, struct ktermios *termios,
 	spin_lock_irqsave(&port->lock, flags);	
 
 	/* Disable IRQs on the port */
-	uap->curregs[R1] &= ~(EXT_INT_ENAB | TxINT_ENAB | RxINT_MASK);
-	write_zsreg(uap, R1, uap->curregs[R1]);
+	pmz_interrupt_control(uap, 0);
 
 	/* Setup new port configuration */
 	__pmz_set_termios(port, termios, old);
 
 	/* Re-enable IRQs on the port */
-	if (ZS_IS_OPEN(uap)) {
-		uap->curregs[R1] |= INT_ALL_Rx | TxINT_ENAB;
-		if (!ZS_IS_EXTCLK(uap))
-			uap->curregs[R1] |= EXT_INT_ENAB;
-		write_zsreg(uap, R1, uap->curregs[R1]);
-	}
+	if (ZS_IS_OPEN(uap))
+		pmz_interrupt_control(uap, 1);
+
 	spin_unlock_irqrestore(&port->lock, flags);
 }
 
@@ -1671,14 +1672,17 @@ static int pmz_suspend(struct macio_dev *mdev, pm_message_t pm_state)
 	spin_lock_irqsave(&uap->port.lock, flags);
 
 	if (ZS_IS_OPEN(uap) || ZS_IS_CONS(uap)) {
-		/* Disable receiver and transmitter.  */
+		/* Disable interrupt requests for the channel */
+		pmz_interrupt_control(uap, 0);
+
+		/* Disable receiver and transmitter */
 		uap->curregs[R3] &= ~RxENABLE;
 		uap->curregs[R5] &= ~TxENABLE;
 
-		/* Disable all interrupts and BRK assertion.  */
-		uap->curregs[R1] &= ~(EXT_INT_ENAB | TxINT_ENAB | RxINT_MASK);
+		/* Disable break assertion */
 		uap->curregs[R5] &= ~SND_BRK;
 		pmz_load_zsregs(uap, uap->curregs);
+
 		uap->flags |= PMACZILOG_FLAG_IS_ASLEEP;
 		mb();
 	}
@@ -1738,14 +1742,6 @@ static int pmz_resume(struct macio_dev *mdev)
 	/* Take care of config that may have changed while asleep */
 	__pmz_set_termios(&uap->port, &uap->termios_cache, NULL);
 
-	if (ZS_IS_OPEN(uap)) {
-		/* Enable interrupts */		
-		uap->curregs[R1] |= INT_ALL_Rx | TxINT_ENAB;
-		if (!ZS_IS_EXTCLK(uap))
-			uap->curregs[R1] |= EXT_INT_ENAB;
-		write_zsreg(uap, R1, uap->curregs[R1]);
-	}
-
 	spin_unlock_irqrestore(&uap->port.lock, flags);
 
 	if (ZS_IS_CONS(uap))
@@ -1757,6 +1753,12 @@ static int pmz_resume(struct macio_dev *mdev)
 		enable_irq(uap->port.irq);
 	}
 
+	if (ZS_IS_OPEN(uap)) {
+		spin_lock_irqsave(&uap->port.lock, flags);
+		pmz_interrupt_control(uap, 1);
+		spin_unlock_irqrestore(&uap->port.lock, flags);
+	}
+
  bail:
 	mutex_unlock(&state->port.mutex);
 	mutex_unlock(&pmz_irq_mutex);