tty/serial: pl011: add generic earlycon support

Add earlycon support for the pl011 serial port. This allows enabling
the pl011 for console when early_params are processed. This is based
on the arm64 earlyprintk support and is intended to replace it.
Signed-off-by: Rob Herring <robh@kernel.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/kernel-parameters.txt

@@ -883,6 +883,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			which are not unmapped.
 
 	earlycon=	[KNL] Output early console device and options.
+
 		uart[8250],io,<addr>[,options]
 		uart[8250],mmio,<addr>[,options]
 		uart[8250],mmio32,<addr>[,options]
@@ -892,6 +893,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			(mmio) or 32-bit (mmio32).
 			The options are the same as for ttyS, above.
 
+		pl011,<addr>
+			Start an early, polled-mode console on a pl011 serial
+			port at the specified address. The pl011 serial port
+			must already be setup and configured. Options are not
+			yet supported.
+
 	earlyprintk=	[X86,SH,BLACKFIN,ARM]
 			earlyprintk=vga
 			earlyprintk=efi

drivers/tty/serial/Kconfig

@@ -60,6 +60,7 @@ config SERIAL_AMBA_PL011_CONSOLE
 	bool "Support for console on AMBA serial port"
 	depends on SERIAL_AMBA_PL011=y
 	select SERIAL_CORE_CONSOLE
+	select SERIAL_EARLYCON
 	---help---
 	  Say Y here if you wish to use an AMBA PrimeCell UART as the system
 	  console (the system console is the device which receives all kernel

drivers/tty/serial/amba-pl011.c

@@ -303,7 +303,7 @@ static void pl011_dma_probe_initcall(struct device *dev, struct uart_amba_port *
 
 	/* Optionally make use of an RX channel as well */
 	chan = dma_request_slave_channel(dev, "rx");
-	
+
 	if (!chan && plat->dma_rx_param) {
 		chan = dma_request_channel(mask, plat->dma_filter, plat->dma_rx_param);
 
@@ -2045,6 +2045,34 @@ static struct console amba_console = {
 };
 
 #define AMBA_CONSOLE	(&amba_console)
+
+static void pl011_putc(struct uart_port *port, int c)
+{
+	while (readl(port->membase + UART01x_FR) & UART01x_FR_TXFF)
+		;
+	writeb(c, port->membase + UART01x_DR);
+	while (readl(port->membase + UART01x_FR) & UART01x_FR_BUSY)
+		;
+}
+
+static void pl011_early_write(struct console *con, const char *s, unsigned n)
+{
+	struct earlycon_device *dev = con->data;
+
+	uart_console_write(&dev->port, s, n, pl011_putc);
+}
+
+static int __init pl011_early_console_setup(struct earlycon_device *device,
+					    const char *opt)
+{
+	if (!device->port.membase)
+		return -ENODEV;
+
+	device->con->write = pl011_early_write;
+	return 0;
+}
+EARLYCON_DECLARE(pl011, pl011_early_console_setup);
+
 #else
 #define AMBA_CONSOLE	NULL
 #endif