spl: add a 'return to bootrom' boot method

Some devices (e.g. the RK3368) have only limited SRAM, but provide
support for loading the next boot stage after our SPL performs basic
setup (e.g. DRAM).

For target systems like these, we add a boot device BOOTROM that will
invoke a board-specific hook to return to the bootrom (if supported).

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>

Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/arm/include/asm/spl.h

@@ -30,6 +30,7 @@ enum {
 	BOOT_DEVICE_BOARD,
 	BOOT_DEVICE_DFU,
 	BOOT_DEVICE_XIP,
+	BOOT_DEVICE_BOOTROM,
 	BOOT_DEVICE_NONE
 };
 #endif

common/spl/Kconfig

@@ -25,6 +25,17 @@ config SPL_BOARD_INIT
 	  spl_board_init() from board_init_r(). This function should be
 	  provided by the board.
 
+config SPL_BOOTROM_SUPPORT
+        bool "Support returning to the BOOTROM"
+	help
+	  Some platforms (e.g. the Rockchip RK3368) provide support in their
+	  ROM for loading the next boot-stage after performing basic setup
+	  from the SPL stage.
+
+	  Enable this option, to return to the BOOTROM through the
+	  BOOT_DEVICE_BOOTROM (or fall-through to the next boot device in the
+	  boot device list, if not implemented for a given board)
+
 config SPL_RAW_IMAGE_SUPPORT
 	bool "Support SPL loading and booting of RAW images"
 	default n if (ARCH_MX6 && (SPL_MMC_SUPPORT || SPL_SATA_SUPPORT))

common/spl/Makefile

@@ -10,6 +10,7 @@
 
 ifdef CONFIG_SPL_BUILD
 obj-$(CONFIG_SPL_FRAMEWORK) += spl.o
+obj-$(CONFIG_SPL_BOOTROM_SUPPORT) += spl_bootrom.o
 obj-$(CONFIG_SPL_LOAD_FIT) += spl_fit.o
 obj-$(CONFIG_SPL_NOR_SUPPORT) += spl_nor.o
 obj-$(CONFIG_SPL_XIP_SUPPORT) += spl_xip.o

common/spl/spl_bootrom.c

@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2017 Theobroma Systems Design und Consulting GmH
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <spl.h>
+
+__weak void board_return_to_bootrom(void)
+{
+}
+
+static int spl_return_to_bootrom(struct spl_image_info *spl_image,
+				 struct spl_boot_device *bootdev)
+{
+	/*
+	 * If the board implements a way to return to its ROM (with
+	 * the expectation that the next stage of will be booted by
+	 * the ROM), it will implement board_return_to_bootrom() and
+	 * should not return from it.
+	 */
+	board_return_to_bootrom();
+	return false;
+}
+
+SPL_LOAD_IMAGE_METHOD("BOOTROM", 0, BOOT_DEVICE_BOOTROM, spl_return_to_bootrom);

include/spl.h

@@ -268,4 +268,14 @@ int spl_mmc_load_image(struct spl_image_info *spl_image,
 		       struct spl_boot_device *bootdev);
 
 void bl31_entry(void);
+
+/**
+ * board_return_to_bootrom - allow for boards to continue with the boot ROM
+ *
+ * If a board (e.g. the Rockchip RK3368 boards) provide some
+ * supporting functionality for SPL in their boot ROM and the SPL
+ * stage wants to return to the ROM code to continue booting, boards
+ * can implement 'board_return_to_bootrom'.
+ */
+void board_return_to_bootrom(void);
 #endif