sunxi: Add arm64 FEL support
So far we did not support the BootROM based FEL USB debug mode on the
64-bit builds for Allwinner SoCs: The BootROM is using AArch32, but the
SPL runs in AArch64.
Returning back to AArch32 was not working as expected, since the RMR
reset into 32-bit mode always starts execution in the BootROM, but not
in the FEL routine.
After some debug and research and with help via IRC, the CPU hotplug
mechanism emerged as a solution: If a certain R_CPUCFG register contains
some magic, the BootROM will immediately branch to an address stored in
some other register. This works well for our purposes.
Enable the FEL feature by providing early AArch32 code to first save the
FEL state, *before* initially entering AArch64.
If we eventually determine that we should return to FEL, we reset back
into AArch32, and use the CPU hotplug mechanism to run some small
AArch32 code snippet that restores the initially saved FEL state.
That allows the normal AArch64 SPL build to be loaded via the sunxi-fel
tool, with it returning into FEL mode, so that other payloads can be
transferred via FEL as well.
Tested on A64, H5 and H6.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Tested-by: Icenowy Zheng <icenowy@aosc.io>
Acked-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Priit Laes <plaes@plaes.org> (on Olimex A64-Olinuxino)
diff --git a/arch/arm/cpu/armv8/Makefile b/arch/arm/cpu/armv8/Makefile
index 93d26f9..f7b4a5e 100644
--- a/arch/arm/cpu/armv8/Makefile
+++ b/arch/arm/cpu/armv8/Makefile
@@ -27,6 +27,8 @@
ifndef CONFIG_SPL_BUILD
obj-$(CONFIG_ARMV8_SPIN_TABLE) += spin_table.o spin_table_v8.o
+else
+obj-$(CONFIG_ARCH_SUNXI) += fel_utils.o
endif
obj-$(CONFIG_$(SPL_)ARMV8_SEC_FIRMWARE_SUPPORT) += sec_firmware.o sec_firmware_asm.o
diff --git a/arch/arm/cpu/armv8/fel_utils.S b/arch/arm/cpu/armv8/fel_utils.S
new file mode 100644
index 0000000..9510dcd
--- /dev/null
+++ b/arch/arm/cpu/armv8/fel_utils.S
@@ -0,0 +1,78 @@
+/*
+ * Utility functions for FEL mode, when running SPL in AArch64.
+ *
+ * Copyright (c) 2017 Arm Ltd.
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ */
+
+#include <asm-offsets.h>
+#include <config.h>
+#include <asm/system.h>
+#include <linux/linkage.h>
+
+/*
+ * We don't overwrite save_boot_params() here, to save the FEL state upon
+ * entry, since this would run *after* the RMR reset, which clobbers that
+ * state.
+ * Instead we store the state _very_ early in the boot0 hook, *before*
+ * resetting to AArch64.
+ */
+
+/*
+ * The FEL routines in BROM run in AArch32.
+ * Reset back into 32-bit mode here and restore the saved FEL state
+ * afterwards.
+ * Resetting back into AArch32/EL3 using the RMR always enters the BROM,
+ * but we can use the CPU hotplug mechanism to branch back to our code
+ * immediately.
+ */
+ENTRY(return_to_fel)
+ /*
+ * the RMR reset will clear all registers, so save the arguments
+ * (LR and SP) in the fel_stash structure, which we read anyways later
+ */
+ adr x2, fel_stash
+ str w0, [x2]
+ str w1, [x2, #4]
+
+ adr x1, fel_stash_addr // to find the fel_stash address in AA32
+ str w2, [x1]
+
+ ldr x0, =0xfa50392f // CPU hotplug magic
+#ifdef CONFIG_MACH_SUN50I_H6
+ ldr x2, =(SUNXI_RTC_BASE + 0x1b8) // BOOT_CPU_HP_FLAG_REG
+ str w0, [x2], #0x4
+#else
+ ldr x2, =(SUNXI_CPUCFG_BASE + 0x1a4) // offset for CPU hotplug base
+ str w0, [x2, #0x8]
+#endif
+ adr x0, back_in_32
+ str w0, [x2]
+
+ dsb sy
+ isb sy
+ mov x0, #2 // RMR reset into AArch32
+ dsb sy
+ msr RMR_EL3, x0
+ isb sy
+1: wfi
+ b 1b
+
+/* AArch32 code to restore the state from fel_stash and return back to FEL. */
+back_in_32:
+ .word 0xe59f0028 // ldr r0, [pc, #40] ; load fel_stash address
+ .word 0xe5901008 // ldr r1, [r0, #8]
+ .word 0xe129f001 // msr CPSR_fc, r1
+ .word 0xf57ff06f // isb
+ .word 0xe590d000 // ldr sp, [r0]
+ .word 0xe590e004 // ldr lr, [r0, #4]
+ .word 0xe5901010 // ldr r1, [r0, #16]
+ .word 0xee0c1f10 // mcr 15, 0, r1, cr12, cr0, {0} ; VBAR
+ .word 0xe590100c // ldr r1, [r0, #12]
+ .word 0xee011f10 // mcr 15, 0, r1, cr1, cr0, {0} ; SCTLR
+ .word 0xf57ff06f // isb
+ .word 0xe12fff1e // bx lr ; return to FEL
+fel_stash_addr:
+ .word 0x00000000 // receives fel_stash addr, by AA64 code above
+ENDPROC(return_to_fel)