[U-Boot] Exception Level switching seems broken on RK3399

[Vicente Bergas]

Hello,
I am writing this from a standalone Sapphire board [1],
 that is, without the Excavator base board.
The CPU is the Rockchip RK3399, which implements ARMv8.0-A.

Currently the boot process is:
 1.- Boot ROM
 2.- SPL, provided as closed source binary blob [2]
 3.- ATF, closed source binary blob [3]
     (not using the one from [2] because of stability issues)
 4.- Mainline u-boot, master branch
 5.- Mainline linux, master branch

I would like to use an opensource boot process.
As a first approach I try to completely remove the ATF and
replace the SPL with the one from u-boot.
The modified boot process looks like:
 1.- Boot ROM
 2.- SPL, from mainline u-boot, master branch
 3.- Mainline u-boot, master branch
 4.- Mainline linux, master branch
But it is not working.

The replaced SPL works fine and loads u-boot.
U-boot also works fine, loads linux and jumps into it.
But then, linux never gets executed.

I have traced the issue to: arch/arm/include/asm/macro.h
 202: msr  spsr_el3, \tmp
 203: msr  elr_el3, \ep
 204: eret // This is the last instruction executed

For testing, I have also set CONFIG_ARMV8_SWITCH_TO_EL1 and
checked that switch_to_el1 from arch/arm/lib/bootm.c is not reached.

At this point I have a few questions:
 1.- Is my first approach feasible? That is, is it possible to boot
     this CPU without ATF?
 2.- If so, what should I do to make it work? Probably it is just
     a configuration issue, but I do not know what to check. [4]
 3.- Else, why do I need ATF?

Regards,
  Vicenç.

[1] http://opensource.rock-chips.com/wiki_Excavator_sapphire_board
[2] https://github.com/rockchip-linux/rkbin/tree/29mirror
[3] https://raw.githubusercontent.com/nightseas/armbian-build/master/packages/blobs/rockchip64/trust.img
[4]
CONFIG_ARM=y
CONFIG_ARCH_ROCKCHIP=y
CONFIG_SYS_TEXT_BASE=0x00200000
CONFIG_SPL_LIBCOMMON_SUPPORT=y
CONFIG_SPL_LIBGENERIC_SUPPORT=y
CONFIG_SYS_MALLOC_F_LEN=0x4000
CONFIG_ROCKCHIP_RK3399=y
CONFIG_ROCKCHIP_SPL_RESERVE_IRAM=0x4000
CONFIG_SPL_STACK_R_ADDR=0x80000
# CONFIG_PSCI_RESET is not set
CONFIG_CMD_HDMIDETECT=y
CONFIG_DEFAULT_DEVICE_TREE="rk3399-evb"
CONFIG_DEBUG_UART=y
CONFIG_BOOTDELAY=1
# CONFIG_DISPLAY_CPUINFO is not set
# CONFIG_DISPLAY_BOARDINFO is not set
CONFIG_SPL_STACK_R=y
CONFIG_SPL_STACK_R_MALLOC_SIMPLE_LEN=0x4000
# CONFIG_CMD_IMI is not set
# CONFIG_CMD_XIMG is not set
# CONFIG_CMD_SAVEENV is not set
# CONFIG_CMD_FLASH is not set
# CONFIG_CMD_LOADB is not set
# CONFIG_CMD_LOADS is not set
CONFIG_CMD_MMC=y
CONFIG_CMD_USB=y
# CONFIG_CMD_SETEXPR is not set
# CONFIG_CMD_NET is not set
# CONFIG_DOS_PARTITION is not set
# CONFIG_ISO_PARTITION is not set
CONFIG_SPL_OF_CONTROL=y
CONFIG_REGMAP=y
CONFIG_SPL_REGMAP=y
CONFIG_SYSCON=y
CONFIG_SPL_SYSCON=y
CONFIG_CLK=y
CONFIG_SPL_CLK=y
CONFIG_ROCKCHIP_GPIO=y
CONFIG_SYS_I2C_ROCKCHIP=y
# CONFIG_MMC_WRITE is not set
# CONFIG_MMC_HW_PARTITIONING is not set
CONFIG_MMC_DW=y
CONFIG_MMC_SDHCI=y
CONFIG_MMC_SDHCI_ROCKCHIP=y
CONFIG_DM_ETH=y
# CONFIG_NETDEVICES is not set
CONFIG_PINCTRL=y
CONFIG_SPL_PINCTRL=y
CONFIG_PINCTRL_ROCKCHIP_RK3399=y
CONFIG_DM_PMIC=y
CONFIG_PMIC_RK8XX=y
CONFIG_REGULATOR_PWM=y
CONFIG_DM_REGULATOR_FIXED=y
CONFIG_REGULATOR_RK8XX=y
CONFIG_PWM_ROCKCHIP=y
CONFIG_RAM=y
CONFIG_SPL_RAM=y
CONFIG_BAUDRATE=1500000
CONFIG_DEBUG_UART_BASE=0xFF1A0000
CONFIG_DEBUG_UART_CLOCK=24000000
CONFIG_DEBUG_UART_SHIFT=2
CONFIG_SYSRESET=y
CONFIG_USB=y
CONFIG_USB_XHCI_HCD=y
CONFIG_USB_XHCI_DWC3=y
CONFIG_USB_EHCI_HCD=y
CONFIG_USB_EHCI_GENERIC=y
CONFIG_USB_STORAGE=y
CONFIG_USB_KEYBOARD=y
CONFIG_USB_HOST_ETHER=y
CONFIG_USB_ETHER_ASIX=y
CONFIG_USB_ETHER_ASIX88179=y
CONFIG_USB_ETHER_MCS7830=y
CONFIG_USB_ETHER_RTL8152=y
CONFIG_USB_ETHER_SMSC95XX=y
CONFIG_DM_VIDEO=y
# CONFIG_BACKLIGHT_PWM is not set
# CONFIG_VIDEO_BPP8 is not set
# CONFIG_VIDEO_BPP16 is not set
# CONFIG_VIDEO_BPP32 is not set
# CONFIG_VIDEO_ANSI is not set
# CONFIG_SYS_WHITE_ON_BLACK is not set
CONFIG_DISPLAY=y
CONFIG_VIDEO_ROCKCHIP=y
CONFIG_DISPLAY_ROCKCHIP_HDMI=y
# CONFIG_FAT_WRITE is not set
CONFIG_USE_TINY_PRINTF=y
CONFIG_ERRNO_STR=y
# CONFIG_EFI_LOADER is not set