x86: coreboot: Add generic coreboot payload support

Currently building U-Boot as the coreboot payload requires user
to change the build configuration for a specific board during
menuconfig process. This uses the board's native device tree
to configure the hardware. For example, the device tree provides
PCI address range for the PCI host controller and U-Boot will
re-program all PCI devices' BAR to be within this range. In order
to make sure we don't mess up the hardware, we should guarantee
the range matches what coreboot programs the chipset.

But we really should make the coreboot payload support easier.
Just like EFI payload, we can create a generic coreboot payload
for all x86 boards as well. The payload is configured to include
as many generic drivers as possible. All stuff that touches low
level initialization are not allowed as such is the coreboot's
responsibility. Platform specific drivers (like gpio, spi, etc)
are not included.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>

board/coreboot/coreboot/Kconfig

@@ -9,35 +9,15 @@ config SYS_VENDOR
 config SYS_SOC
 	default "coreboot"
 
+config SYS_CONFIG_NAME
+	default "coreboot"
+
 config SYS_TEXT_BASE
 	default 0x01110000
 
 config BOARD_SPECIFIC_OPTIONS # dummy
 	def_bool y
-	imply SPI_FLASH_ATMEL
-	imply SPI_FLASH_EON
-	imply SPI_FLASH_GIGADEVICE
-	imply SPI_FLASH_MACRONIX
-	imply SPI_FLASH_SPANSION
-	imply SPI_FLASH_STMICRO
-	imply SPI_FLASH_SST
-	imply SPI_FLASH_WINBOND
-
-comment "coreboot-specific options"
-
-config SYS_CONFIG_NAME
-	string "Board configuration file"
-	default "qemu-x86"
-	help
-	  This option selects the board configuration file in include/configs/
-	  directory to be used to build U-Boot for coreboot.
-
-config DEFAULT_DEVICE_TREE
-	string "Board Device Tree Source (dts) file"
-	default "qemu-x86_i440fx"
-	help
-	  This option selects the board Device Tree Source (dts) file in
-	  arch/x86/dts/ directory to be used to build U-Boot for coreboot.
+	select BOARD_EARLY_INIT_R
 
 config SYS_CAR_ADDR
 	hex "Board specific Cache-As-RAM (CAR) address"

board/coreboot/coreboot/Makefile

@@ -10,4 +10,4 @@
 # (C) Copyright 2002
 # Daniel Engström, Omicron Ceti AB, daniel@omicron.se.
 
-obj-y	+= coreboot_start.o
+obj-y	+= start.o coreboot.o

board/coreboot/coreboot/coreboot.c

@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2018, Bin Meng <bmeng.cn@gmail.com>
+ */
+
+#include <common.h>
+
+int board_early_init_r(void)
+{
+	/*
+	 * Make sure PCI bus is enumerated so that peripherals on the PCI bus
+	 * can be discovered by their drivers
+	 */
+	pci_init();
+
+	return 0;
+}