[RFC][PATCH] Way for platforms to alter built-in serial ports

[Benjamin Herrenschmidt]

Hi Russel !

I'm back with a finally useable fix for an oooooold problem, which is
the way the serial table is supposed to be hard coded in asm/serial.h
makes it really nasty to deal with for platforms like ppc where a
given kernel can boot machines with different setups or even no
built-in serial port at all.

(I currently have the 3 cases on ppc64: some normal ISA serial, some
with different port/irq settings, and machines with no ports at all,
all in the same kernel image).

The early_serial_setup() thing has never been practical to use, since
it basically consist of "shoving" entries into the table, which is a
bit ugly, requires knowledge of the table size if we want to remove
all entries but N, that sort of thing, but the MAIN issue is that it's
fundamentally incompatible with the driver beeing in a module.

What I propose is a way for the arch to provide it's own table along
with the size of it via a function call. It's optional, based on a
#ifdef defined by the arch in it's asm/serial.h. The only remaining
tricky point is the fact that you used to size your static array of
UART's based on the size of the table. So with my path, an arch
that defines ARCH_HAS_GET_LEGACY_SERIAL_PORTS is supposed to provide
both the new get_legacy_serial_ports() function, but also to define
UART_NR to something sensible. I hope one day, we'll be able to
convert 8250 to more dynamic allocation though.

With this patch, I fix all my problems of properly detecting built-in
serial ports _and_ not munging around with non existing ports on machines
with no legacy HW with a single kernel image on ppc64 (and hopefully on
ppc32 too). I have the ppc64-side of the patch beeing tested on various
hardware at the moment and will submit it if you accept this one.

Regards,
Ben.

Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>

diff -urN linux-2.5/drivers/serial/8250.c linux-maple/drivers/serial/8250.c
--- linux-2.5/drivers/serial/8250.c	2004-09-30 18:31:42.560719874 +1000
+++ linux-maple/drivers/serial/8250.c	2004-09-30 16:27:39.421941590 +1000
@@ -112,11 +112,18 @@
 #define SERIAL_PORT_DFNS
 #endif
 
+#ifndef ARCH_HAS_GET_LEGACY_SERIAL_PORTS
 static struct old_serial_port old_serial_port[] = {
 	SERIAL_PORT_DFNS /* defined in asm/serial.h */
 };
-
+static inline struct old_serial_port *get_legacy_serial_ports(unsigned int *count)
+{
+	*count = ARRAY_SIZE(old_serial_port);
+	return old_serial_port;
+}
 #define UART_NR	(ARRAY_SIZE(old_serial_port) + CONFIG_SERIAL_8250_NR_UARTS)
+#endif /* ARCH_HAS_GET_LEGACY_SERIAL_PORTS */
+
 
 #ifdef CONFIG_SERIAL_8250_RSA
 
@@ -1839,22 +1846,28 @@
 {
 	struct uart_8250_port *up;
 	static int first = 1;
+	struct old_serial_port *old_ports;
+	int count;
 	int i;
 
 	if (!first)
 		return;
 	first = 0;
 
-	for (i = 0, up = serial8250_ports; i < ARRAY_SIZE(old_serial_port);
+	old_ports = get_legacy_serial_ports(&count);
+	if (old_ports == NULL)
+		return;
+
+	for (i = 0, up = serial8250_ports; i < count;
 	     i++, up++) {
-		up->port.iobase   = old_serial_port[i].port;
-		up->port.irq      = irq_canonicalize(old_serial_port[i].irq);
-		up->port.uartclk  = old_serial_port[i].baud_base * 16;
-		up->port.flags    = old_serial_port[i].flags;
-		up->port.hub6     = old_serial_port[i].hub6;
-		up->port.membase  = old_serial_port[i].iomem_base;
-		up->port.iotype   = old_serial_port[i].io_type;
-		up->port.regshift = old_serial_port[i].iomem_reg_shift;
+		up->port.iobase   = old_ports[i].port;
+		up->port.irq      = irq_canonicalize(old_ports[i].irq);
+		up->port.uartclk  = old_ports[i].baud_base * 16;
+		up->port.flags    = old_ports[i].flags;
+		up->port.hub6     = old_ports[i].hub6;
+		up->port.membase  = old_ports[i].iomem_base;
+		up->port.iotype   = old_ports[i].io_type;
+		up->port.regshift = old_ports[i].iomem_reg_shift;
 		up->port.ops      = &serial8250_pops;
 		if (share_irqs)
 			up->port.flags |= UPF_SHARE_IRQ;
diff -urN linux-2.5/drivers/serial/8250.h linux-maple/drivers/serial/8250.h
--- linux-2.5/drivers/serial/8250.h	2004-09-30 18:31:42.561719806 +1000
+++ linux-maple/drivers/serial/8250.h	2004-09-30 15:36:55.867448623 +1000
@@ -21,18 +21,6 @@
 void serial8250_suspend_port(int line);
 void serial8250_resume_port(int line);
 
-struct old_serial_port {
-	unsigned int uart;
-	unsigned int baud_base;
-	unsigned int port;
-	unsigned int irq;
-	unsigned int flags;
-	unsigned char hub6;
-	unsigned char io_type;
-	unsigned char *iomem_base;
-	unsigned short iomem_reg_shift;
-};
-
 /*
  * This replaces serial_uart_config in include/linux/serial.h
  */
diff -urN linux-2.5/include/linux/serial.h linux-maple/include/linux/serial.h
--- linux-2.5/include/linux/serial.h	2004-09-30 18:31:55.867785437 +1000
+++ linux-maple/include/linux/serial.h	2004-09-30 15:36:57.981697919 +1000
@@ -14,6 +14,21 @@
 #include <asm/page.h>
 
 /*
+ * Definition of a legacy serial port
+ */
+struct old_serial_port {
+	unsigned int uart;
+	unsigned int baud_base;
+	unsigned int port;
+	unsigned int irq;
+	unsigned int flags;
+	unsigned char hub6;
+	unsigned char io_type;
+	unsigned char *iomem_base;
+	unsigned short iomem_reg_shift;
+};
+
+/*
  * Counters of the input lines (CTS, DSR, RI, CD) interrupts
  */