serial: support 16-bit register interface for console

Currently, 8-bit (MMIO) and 32-bit (MMIO32) register interfaces are
supported for the 8250 console, but the 16-bit (MMIO16) is not.
The 8250 UART device on my board is connected to a 16-bit bus and
my main motivation is to use earlycon with it.
(Refer to arch/arm/boot/dts/uniphier-support-card.dtsi)

Signed-off-by: Masahiro Yamada <[e-mail]>
Reviewed-by: Peter Hurley <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/kernel-parameters.txt

···
 
 		uart[8250],io,<addr>[,options]
 		uart[8250],mmio,<addr>[,options]
+		uart[8250],mmio16,<addr>[,options]
 		uart[8250],mmio32,<addr>[,options]
 		uart[8250],0x<addr>[,options]
 			Start an early, polled-mode console on the 8250/16550
 			UART at the specified I/O port or MMIO address,
 			switching to the matching ttyS device later.
 			MMIO inter-register address stride is either 8-bit
-			(mmio) or 32-bit (mmio32).
-			If none of [io|mmio|mmio32], <addr> is assumed to be
-			equivalent to 'mmio'. 'options' are specified in the
-			same format described for ttyS above; if unspecified,
+			(mmio), 16-bit (mmio16), or 32-bit (mmio32).
+			If none of [io|mmio|mmio16|mmio32], <addr> is assumed
+			to be equivalent to 'mmio'. 'options' are specified in
+			the same format described for ttyS above; if unspecified,
 			the h/w is not re-initialized.
 
 		hvc<n>	Use the hypervisor console device <n>. This is for

drivers/tty/serial/8250/8250_core.c

···
  *	@options: ptr to option string from console command line
  *
  *	Only attempts to match console command lines of the form:
- *	    console=uart[8250],io|mmio|mmio32,<addr>[,<options>]
+ *	    console=uart[8250],io|mmio|mmio16|mmio32,<addr>[,<options>]
  *	    console=uart[8250],0x<addr>[,<options>]
  *	This form is used to register an initial earlycon boot console and
  *	replace it with the serial8250_console at 8250 driver init.
···
 
 		if (port->iotype != iotype)
 			continue;
-		if ((iotype == UPIO_MEM || iotype == UPIO_MEM32) &&
-		    (port->mapbase != addr))
+		if ((iotype == UPIO_MEM || iotype == UPIO_MEM16 ||
+		     iotype == UPIO_MEM32 || iotype == UPIO_MEM32BE)
+		    && (port->mapbase != addr))
 			continue;
 		if (iotype == UPIO_PORT && port->iobase != addr)
 			continue;

drivers/tty/serial/8250/8250_early.c

···
 	switch (port->iotype) {
 	case UPIO_MEM:
 		return readb(port->membase + offset);
+	case UPIO_MEM16:
+		return readw(port->membase + (offset << 1));
 	case UPIO_MEM32:
 		return readl(port->membase + (offset << 2));
 	case UPIO_MEM32BE:
···
 	switch (port->iotype) {
 	case UPIO_MEM:
 		writeb(value, port->membase + offset);
+		break;
+	case UPIO_MEM16:
+		writew(value, port->membase + (offset << 1));
 		break;
 	case UPIO_MEM32:
 		writel(value, port->membase + (offset << 2));

drivers/tty/serial/8250/8250_port.c

···
 	writeb(value, p->membase + offset);
 }
 
+static void mem16_serial_out(struct uart_port *p, int offset, int value)
+{
+	offset = offset << p->regshift;
+	writew(value, p->membase + offset);
+}
+
+static unsigned int mem16_serial_in(struct uart_port *p, int offset)
+{
+	offset = offset << p->regshift;
+	return readw(p->membase + offset);
+}
+
 static void mem32_serial_out(struct uart_port *p, int offset, int value)
 {
 	offset = offset << p->regshift;
···
 		p->serial_out = mem_serial_out;
 		break;
 
+	case UPIO_MEM16:
+		p->serial_in = mem16_serial_in;
+		p->serial_out = mem16_serial_out;
+		break;
+
 	case UPIO_MEM32:
 		p->serial_in = mem32_serial_in;
 		p->serial_out = mem32_serial_out;
···
 {
 	switch (p->iotype) {
 	case UPIO_MEM:
+	case UPIO_MEM16:
 	case UPIO_MEM32:
 	case UPIO_MEM32BE:
 	case UPIO_AU:
···
 	case UPIO_TSI:
 	case UPIO_MEM32:
 	case UPIO_MEM32BE:
+	case UPIO_MEM16:
 	case UPIO_MEM:
 		if (!port->mapbase)
 			break;
···
 	case UPIO_TSI:
 	case UPIO_MEM32:
 	case UPIO_MEM32BE:
+	case UPIO_MEM16:
 	case UPIO_MEM:
 		if (!port->mapbase)
 			break;

drivers/tty/serial/earlycon.c

···
 		return -EINVAL;
 
 	switch (port->iotype) {
+	case UPIO_MEM:
+		port->mapbase = addr;
+		break;
+	case UPIO_MEM16:
+		port->regshift = 1;
+		port->mapbase = addr;
+		break;
 	case UPIO_MEM32:
 	case UPIO_MEM32BE:
-		port->regshift = 2;	/* fall-through */
-	case UPIO_MEM:
+		port->regshift = 2;
 		port->mapbase = addr;
 		break;
 	case UPIO_PORT:
···
 		strlcpy(device->options, options, length);
 	}
 
-	if (port->iotype == UPIO_MEM || port->iotype == UPIO_MEM32 ||
-	    port->iotype == UPIO_MEM32BE)
+	if (port->iotype == UPIO_MEM || port->iotype == UPIO_MEM16 ||
+	    port->iotype == UPIO_MEM32 || port->iotype == UPIO_MEM32BE)
 		pr_info("Early serial console at MMIO%s 0x%llx (options '%s')\n",
 			(port->iotype == UPIO_MEM) ? "" :
+			(port->iotype == UPIO_MEM16) ? "16" :
 			(port->iotype == UPIO_MEM32) ? "32" : "32be",
 			(unsigned long long)port->mapbase,
 			device->options);

drivers/tty/serial/of_serial.c

···
 		case 1:
 			port->iotype = UPIO_MEM;
 			break;
+		case 2:
+			port->iotype = UPIO_MEM16;
+			break;
 		case 4:
 			port->iotype = of_device_is_big_endian(np) ?
 				       UPIO_MEM32BE : UPIO_MEM32;

drivers/tty/serial/serial_core.c

···
  *	@options: ptr for <options> field; NULL if not present (out)
  *
  *	Decodes earlycon kernel command line parameters of the form
- *	   earlycon=<name>,io|mmio|mmio32|mmio32be|mmio32native,<addr>,<options>
- *	   console=<name>,io|mmio|mmio32|mmio32be|mmio32native,<addr>,<options>
+ *	   earlycon=<name>,io|mmio|mmio16|mmio32|mmio32be|mmio32native,<addr>,<options>
+ *	   console=<name>,io|mmio|mmio16|mmio32|mmio32be|mmio32native,<addr>,<options>
  *
  *	The optional form
  *	   earlycon=<name>,0x<addr>,<options>
···
 	if (strncmp(p, "mmio,", 5) == 0) {
 		*iotype = UPIO_MEM;
 		p += 5;
+	} else if (strncmp(p, "mmio16,", 7) == 0) {
+		*iotype = UPIO_MEM16;
+		p += 7;
 	} else if (strncmp(p, "mmio32,", 7) == 0) {
 		*iotype = UPIO_MEM32;
 		p += 7;
···
 			 "I/O 0x%lx offset 0x%x", port->iobase, port->hub6);
 		break;
 	case UPIO_MEM:
+	case UPIO_MEM16:
 	case UPIO_MEM32:
 	case UPIO_MEM32BE:
 	case UPIO_AU:
···
 		return (port1->iobase == port2->iobase) &&
 		       (port1->hub6   == port2->hub6);
 	case UPIO_MEM:
+	case UPIO_MEM16:
 	case UPIO_MEM32:
 	case UPIO_MEM32BE:
 	case UPIO_AU:

include/linux/serial_core.h

···
 #define UPIO_AU			(SERIAL_IO_AU)		/* Au1x00 and RT288x type IO */
 #define UPIO_TSI		(SERIAL_IO_TSI)		/* Tsi108/109 type IO */
 #define UPIO_MEM32BE		(SERIAL_IO_MEM32BE)	/* 32b big endian */
+#define UPIO_MEM16		(SERIAL_IO_MEM16)	/* 16b little endian */
 
 	unsigned int		read_status_mask;	/* driver specific */
 	unsigned int		ignore_status_mask;	/* driver specific */

include/uapi/linux/serial.h

···
 #define SERIAL_IO_AU	  4
 #define SERIAL_IO_TSI	  5
 #define SERIAL_IO_MEM32BE 6
+#define SERIAL_IO_MEM16	7
 
 #define UART_CLEAR_FIFO		0x01
 #define UART_USE_FIFO		0x02