serial: define FIXED_PORT flag for serial_core

At present, the serial core always allows setserial in userspace to change the
port address, irq and base clock of any serial port.  That makes sense for
legacy ISA ports, but not for (say) embedded ns16550 compatible serial ports
at peculiar addresses.  In these cases, the kernel code configuring the ports
must know exactly where they are, and their clocking arrangements (which can
be unusual on embedded boards).  It doesn't make sense for userspace to change
these settings.

Therefore, this patch defines a UPF_FIXED_PORT flag for the uart_port
structure.  If this flag is set when the serial port is configured, any
attempts to alter the port's type, io address, irq or base clock with
setserial are ignored.

In addition this patch uses the new flag for on-chip serial ports probed in
arch/powerpc/kernel/legacy_serial.c, and for other hard-wired serial ports
probed by drivers/serial/of_serial.c.

Signed-off-by: David Gibson <dwg@au1.ibm.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 15 insertions, 10 deletions

diff --git a/drivers/serial/of_serial.c b/drivers/serial/of_serial.c
index 09b0b73..336d0f4 100644
--- a/drivers/serial/of_serial.c
+++ b/drivers/serial/of_serial.c
@@ -48,7 +48,8 @@ static int __devinit of_platform_serial_setup(struct of_device *ofdev,
 	port->iotype = UPIO_MEM;
 	port->type = type;
 	port->uartclk = *clk;
-	port->flags = UPF_SHARE_IRQ | UPF_BOOT_AUTOCONF | UPF_IOREMAP;
+	port->flags = UPF_SHARE_IRQ | UPF_BOOT_AUTOCONF | UPF_IOREMAP
+		| UPF_FIXED_PORT;
 	port->dev = &ofdev->dev;
 	port->custom_divisor = *clk / (16 * (*spd));
 
diff --git a/drivers/serial/serial_core.c b/drivers/serial/serial_core.c
index a677133..f409be3 100644
--- a/drivers/serial/serial_core.c
+++ b/drivers/serial/serial_core.c
@@ -672,19 +672,21 @@ static int uart_set_info(struct uart_state *state,
 	 */
 	mutex_lock(&state->mutex);
 
-	change_irq  = new_serial.irq != port->irq;
+	change_irq  = !(port->flags & UPF_FIXED_PORT)
+		&& new_serial.irq != port->irq;
 
 	/*
 	 * Since changing the 'type' of the port changes its resource
 	 * allocations, we should treat type changes the same as
 	 * IO port changes.
 	 */
-	change_port = new_port != port->iobase ||
-		      (unsigned long)new_serial.iomem_base != port->mapbase ||
-		      new_serial.hub6 != port->hub6 ||
-		      new_serial.io_type != port->iotype ||
-		      new_serial.iomem_reg_shift != port->regshift ||
-		      new_serial.type != port->type;
+	change_port = !(port->flags & UPF_FIXED_PORT)
+		&& (new_port != port->iobase ||
+		    (unsigned long)new_serial.iomem_base != port->mapbase ||
+		    new_serial.hub6 != port->hub6 ||
+		    new_serial.io_type != port->iotype ||
+		    new_serial.iomem_reg_shift != port->regshift ||
+		    new_serial.type != port->type);
 
 	old_flags = port->flags;
 	new_flags = new_serial.flags;
@@ -796,8 +798,10 @@ static int uart_set_info(struct uart_state *state,
 		}
 	}
 
-	port->irq              = new_serial.irq;
-	port->uartclk          = new_serial.baud_base * 16;
+	if (change_irq)
+		port->irq      = new_serial.irq;
+	if (!(port->flags & UPF_FIXED_PORT))
+		port->uartclk  = new_serial.baud_base * 16;
 	port->flags            = (port->flags & ~UPF_CHANGE_MASK) |
 				 (new_flags & UPF_CHANGE_MASK);
 	port->custom_divisor   = new_serial.custom_divisor;