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>

arch/powerpc/kernel/legacy_serial.c

@@ -115,7 +115,8 @@ static int __init add_legacy_soc_port(struct device_node *np,
 {
 	u64 addr;
 	const u32 *addrp;
-	upf_t flags = UPF_BOOT_AUTOCONF | UPF_SKIP_TEST | UPF_SHARE_IRQ;
+	upf_t flags = UPF_BOOT_AUTOCONF | UPF_SKIP_TEST | UPF_SHARE_IRQ
+		| UPF_FIXED_PORT;
 	struct device_node *tsi = of_get_parent(np);
 
 	/* We only support ports that have a clock frequency properly

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));
 

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 ||
+	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;
+		    new_serial.type != port->type);
 
 	old_flags = port->flags;
 	new_flags = new_serial.flags;
@@ -796,7 +798,9 @@ static int uart_set_info(struct uart_state *state,
 		}
 	}
 
+	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);

include/linux/serial_core.h

@@ -263,6 +263,7 @@ struct uart_port {
 #define UPF_CONS_FLOW		((__force upf_t) (1 << 23))
 #define UPF_SHARE_IRQ		((__force upf_t) (1 << 24))
 #define UPF_BOOT_AUTOCONF	((__force upf_t) (1 << 28))
+#define UPF_FIXED_PORT		((__force upf_t) (1 << 29))
 #define UPF_DEAD		((__force upf_t) (1 << 30))
 #define UPF_IOREMAP		((__force upf_t) (1 << 31))