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 (file)
--- a/arch/arm/cpu/armv8/Makefile
+++ b/arch/arm/cpu/armv8/Makefile
@@ -27,6 +27,8 @@ obj-$(CONFIG_ARM_SMCCC)               += smccc-call.o
 
 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 (file)
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)

diff --git a/arch/arm/include/asm/arch-sunxi/boot0.h b/arch/arm/include/asm/arch-sunxi/boot0.h
index 54c144a..46d0f06 100644 (file)
--- a/arch/arm/include/asm/arch-sunxi/boot0.h
+++ b/arch/arm/include/asm/arch-sunxi/boot0.h
@@ -15,6 +15,19 @@
        tst     x0, x0                  // this is "b #0x84" in ARM
        b       reset
        .space  0x7c
+
+       .word   0xe28f0058      // add     r0, pc, #88
+       .word   0xe59f1054      // ldr     r1, [pc, #84]
+       .word   0xe0800001      // add     r0, r0, r1
+       .word   0xe580d000      // str     sp, [r0]
+       .word   0xe580e004      // str     lr, [r0, #4]
+       .word   0xe10fe000      // mrs     lr, CPSR
+       .word   0xe580e008      // str     lr, [r0, #8]
+       .word   0xee11ef10      // mrc     15, 0, lr, cr1, cr0, {0}
+       .word   0xe580e00c      // str     lr, [r0, #12]
+       .word   0xee1cef10      // mrc     15, 0, lr, cr12, cr0, {0}
+       .word   0xe580e010      // str     lr, [r0, #16]
+
        .word   0xe59f1024      // ldr     r1, [pc, #36] ; 0x170000a0
        .word   0xe59f0024      // ldr     r0, [pc, #36] ; CONFIG_*_TEXT_BASE
        .word   0xe5810000      // str     r0, [r1]
@@ -36,6 +49,7 @@
 #else
        .word   CONFIG_SYS_TEXT_BASE
 #endif
+       .word   fel_stash - .
 #else
 /* normal execution */
        b       reset

diff --git a/include/configs/sunxi-common.h b/include/configs/sunxi-common.h
index a6a4879..203cb10 100644 (file)
--- a/include/configs/sunxi-common.h
+++ b/include/configs/sunxi-common.h
@@ -163,9 +163,7 @@
 
 #define CONFIG_SYS_MONITOR_LEN         (768 << 10)     /* 768 KiB */
 
-#ifndef CONFIG_ARM64           /* AArch64 FEL support is not ready yet */
 #define CONFIG_SPL_BOARD_LOAD_IMAGE
-#endif
 
 /*
  * We cannot use expressions here, because expressions won't be evaluated in