x86: Support booting SeaBIOS

SeaBIOS is an open source implementation of a 16-bit x86 BIOS.
It can run in an emulator or natively on x86 hardware with the
use of coreboot. With SeaBIOS's help, we can boot some OSes
that require 16-bit BIOS services like Windows/DOS.

As U-Boot, we have to manually create a table where SeaBIOS gets
system information (eg: E820) from. The table unfortunately has
to follow the coreboot table format as SeaBIOS currently supports
booting as a coreboot payload.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/x86/Kconfig

@@ -449,6 +449,16 @@ config I8042_KEYB
 config DM_KEYBOARD
 	default y
 
+config SEABIOS
+	bool "Support booting SeaBIOS"
+	help
+	  SeaBIOS is an open source implementation of a 16-bit X86 BIOS.
+	  It can run in an emulator or natively on X86 hardware with the use
+	  of coreboot/U-Boot. By turning on this option, U-Boot prepares
+	  all the configuration tables that are necessary to boot SeaBIOS.
+
+	  Check http://www.seabios.org/SeaBIOS for details.
+
 source "arch/x86/lib/efi/Kconfig"
 
 endmenu

arch/x86/include/asm/tables.h

@@ -16,6 +16,9 @@
 
 #define ROM_TABLE_ALIGN	1024
 
+/* SeaBIOS expects coreboot tables at address range 0x0000-0x1000 */
+#define CB_TABLE_ADDR	0x800
+
 /**
  * table_compute_checksum() - Compute a table checksum
  *

arch/x86/lib/tables.c

@@ -10,6 +10,7 @@
 #include <asm/smbios.h>
 #include <asm/tables.h>
 #include <asm/acpi_table.h>
+#include <asm/coreboot_tables.h>
 
 /**
  * Function prototype to write a specific configuration table
@@ -67,22 +68,36 @@ void write_tables(void)
 {
 	u32 rom_table_start = ROM_TABLE_ADDR;
 	u32 rom_table_end;
+#ifdef CONFIG_SEABIOS
 	u32 high_table, table_size;
+	struct memory_area cfg_tables[ARRAY_SIZE(table_write_funcs) + 1];
+#endif
 	int i;
 
 	for (i = 0; i < ARRAY_SIZE(table_write_funcs); i++) {
 		rom_table_end = table_write_funcs[i](rom_table_start);
 		rom_table_end = ALIGN(rom_table_end, ROM_TABLE_ALIGN);
 
+#ifdef CONFIG_SEABIOS
 		table_size = rom_table_end - rom_table_start;
 		high_table = (u32)memalign(ROM_TABLE_ALIGN, table_size);
 		if (high_table) {
 			memset((void *)high_table, 0, table_size);
 			table_write_funcs[i](high_table);
+
+			cfg_tables[i].start = high_table;
+			cfg_tables[i].size = table_size;
 		} else {
 			printf("%d: no memory for configuration tables\n", i);
 		}
+#endif
 
 		rom_table_start = rom_table_end;
 	}
+
+#ifdef CONFIG_SEABIOS
+	/* make sure the last item is zero */
+	cfg_tables[i].size = 0;
+	write_coreboot_table(CB_TABLE_ADDR, cfg_tables);
+#endif
 }