powerpc/legacy_serial: Support MVME5100 UARTS with shifted registers

This patch adds support to legacy serial for
UARTS with shifted registers.

The MVME5100 Single Board Computer is a PowerPC platform
that has 16550 style UARTS with register addresses that are
16 bytes apart (shifted by 4).

Commit 309257484cc1a592e8ac5fbdd8cd661be2b80bf8
"powerpc: Cleanup udbg_16550 and add support for LPC PIO-only UARTs"
added support to udbg_16550 for shifted registers by adding a "stride"
parameter to the initialisation operations for Programmed IO and
Memory Mapped IO.

As a consequence it is now possible to use the services of legacy serial
to provide early serial console messages for the MVME5100.

An added benefit of this is that the serial console will always be
"ttyS0" irrespective of whether the computer is fitted with extra
PCI 8250 interface boards or not.

I have tested this patch using the four PowerPC platforms available to me:

MVME5100 - shifted registers,
SAM440EP - unshifted registers,
MPC8349 - unshifted registers,
MVME4100 - unshifted registers.

Signed-off-by: Stephen Chivers <[e-mail]>
Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

arch/powerpc/kernel/legacy_serial.c

···
 				  phys_addr_t taddr, unsigned long irq,
 				  upf_t flags, int irq_check_parent)
 {
-	const __be32 *clk, *spd;
+	const __be32 *clk, *spd, *rs;
 	u32 clock = BASE_BAUD * 16;
+	u32 shift = 0;
 	int index;
 
 	/* get clock freq. if present */
···
 
 	/* get default speed if present */
 	spd = of_get_property(np, "current-speed", NULL);
+
+	/* get register shift if present */
+	rs = of_get_property(np, "reg-shift", NULL);
+	if (rs && *rs)
+		shift = be32_to_cpup(rs);
 
 	/* If we have a location index, then try to use it */
 	if (want_index >= 0 && want_index < MAX_LEGACY_SERIAL_PORTS)
···
 	legacy_serial_ports[index].uartclk = clock;
 	legacy_serial_ports[index].irq = irq;
 	legacy_serial_ports[index].flags = flags;
+	legacy_serial_ports[index].regshift = shift;
 	legacy_serial_infos[index].taddr = taddr;
 	legacy_serial_infos[index].np = of_node_get(np);
 	legacy_serial_infos[index].clock = clock;
···
 	if (of_get_property(np, "clock-frequency", NULL) == NULL)
 		return -1;
 
-	/* if reg-shift or offset, don't try to use it */
-	if ((of_get_property(np, "reg-shift", NULL) != NULL) ||
-		(of_get_property(np, "reg-offset", NULL) != NULL))
+	/* if reg-offset don't try to use it */
+	if ((of_get_property(np, "reg-offset", NULL) != NULL))
 		return -1;
 
 	/* if rtas uses this device, don't try to use it as well */
···
 	struct legacy_serial_info *info = &legacy_serial_infos[console];
 	struct plat_serial8250_port *port = &legacy_serial_ports[console];
 	void __iomem *addr;
+	unsigned int stride;
+
+	stride = 1 << port->regshift;
 
 	/* Check if a translated MMIO address has been found */
 	if (info->taddr) {
 		addr = ioremap(info->taddr, 0x1000);
 		if (addr == NULL)
 			return;
-		udbg_uart_init_mmio(addr, 1);
+		udbg_uart_init_mmio(addr, stride);
 	} else {
 		/* Check if it's PIO and we support untranslated PIO */
 		if (port->iotype == UPIO_PORT && isa_io_special)
-			udbg_uart_init_pio(port->iobase, 1);
+			udbg_uart_init_pio(port->iobase, stride);
 		else
 			return;
 	}

arch/powerpc/platforms/embedded6xx/Kconfig

···
 	select PPC_INDIRECT_PCI
 	select PPC_I8259
 	select PPC_NATIVE
+	select PPC_UDBG_16550
 	help
 	  This option enables support for the Motorola (now Emerson) MVME5100
 	  board.