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

diff --git a/arch/powerpc/kernel/legacy_serial.c b/arch/powerpc/kernel/legacy_serial.c
index 63dd2c3..ae4836e 100644
--- a/arch/powerpc/kernel/legacy_serial.c
+++ b/arch/powerpc/kernel/legacy_serial.c
@@ -115,7 +115,8 @@
 {
 	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

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 @@
 	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

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 @@
 	 */
 	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 @@
 		}
 	}
 
-	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;

include/linux/serial_core.h

diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index d242c73..aadbfd3 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -263,6 +263,7 @@
 #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))