console: add support for QEMU's debugcon

Add support for sending debug output to an I/O port.

It can be used together with QEMU's isa-debugcon driver to log the
coreboot output to a file.  The port is configurable and defaults
to 0x402 which has established as the de facto standard. For example,
SeaBIOS+OVMF [1] use that one too.

[1] http://www.linux-kvm.org/page/OVMF
    Open Virtual Machine Firmware
Change-Id: I0803f7fc70030242f80003e25c9449c37d71975e
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-on: http://review.coreboot.org/3331
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/console/Kconfig

@@ -250,6 +250,23 @@ config CONSOLE_CAR_BUFFER_SIZE
 	  in the DCACHE based RAM to keep console output before it can be
 	  saved in a CBMEM buffer. 3K bytes should be enough even for the
 	  BIOS_SPEW level.
+
+config CONSOLE_DEBUGCON
+	bool "QEMU debug console output"
+	depends on BOARD_EMULATION_QEMU_X86
+	default y
+	help
+	  Send coreboot debug output to QEMU's isa-debugcon device:
+
+	  qemu-system-x86_64 \
+	    -chardev file,id=debugcon,path=/dir/file.log \
+	    -device isa-debugcon,iobase=0x402,chardev=debugcon
+
+config CONSOLE_DEBUGCON_PORT
+	hex "QEMU debug console port"
+	depends on CONSOLE_DEBUGCON
+	default 0x402
+
 choice
 	prompt "Default console log level"
 	default DEFAULT_CONSOLE_LOGLEVEL_8

src/console/Makefile.inc

@@ -25,6 +25,7 @@ ramstage-$(CONFIG_USBDEBUG) += usbdebug_console.c
 ramstage-$(CONFIG_CONSOLE_LOGBUF) += logbuf_console.c
 ramstage-$(CONFIG_CONSOLE_NE2K) += ne2k_console.c
 ramstage-$(CONFIG_CONSOLE_CBMEM) += cbmem_console.c
+ramstage-$(CONFIG_CONSOLE_DEBUGCON) += debugcon_console.c
 
 
 $(obj)/console/console.ramstage.o : $(obj)/build.h

src/console/debugcon_console.c

@@ -0,0 +1,53 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright (C) 2013 Red Hat Inc.
+ * Written by Gerd Hoffmann <kraxel@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <console/console.h>
+#include <arch/io.h>
+
+static void debugcon_init(void)
+{
+}
+
+static void debugcon_tx_byte(unsigned char data)
+{
+	outb(data, CONFIG_CONSOLE_DEBUGCON_PORT);
+}
+
+static void debugcon_tx_flush(void)
+{
+}
+
+static unsigned char debugcon_rx_byte(void)
+{
+	return 0;
+}
+
+static int debugcon_tst_byte(void)
+{
+	return 0;
+}
+
+static const struct console_driver debugcon_console __console = {
+	.init = debugcon_init,
+	.tx_byte = debugcon_tx_byte,
+	.tx_flush = debugcon_tx_flush,
+	.rx_byte = debugcon_rx_byte,
+	.tst_byte = debugcon_tst_byte,
+};