Hi,
i am porting u-boot to a new device:
https://handhelds.wiki/R36S_Handheld_Wiki
Given the similarity with ODROID_GO2, i've based my efforts on it and
all goes fine up to the very last step: jumping from u-boot to linux.
In the file arch/arm/cpu/armv8/transition.S there is a call to
armv8_switch_to_el2_m which is supposed to jump into linux, but it
doesn't.
I've added some debug prints around it (see patch below) and it prints
the first message:
"before switch from EL3 to EL2"
but it does not print either of the messages after.
As another test, i've tried to replace
armv8_switch_to_el2_m x4, x5, x6
to
br x4
and then it indeed switches to linux, but then linux crashes, prints a
trace and reboots, that is, it doesn't like running from EL3.
Please, can somebody help here?
Regards,
Vicente.
--- a/arch/arm/include/asm/macro.h
+++ b/arch/arm/include/asm/macro.h
@@ -209,6 +209,7 @@
msr spsr_el3, \tmp
msr elr_el3, \ep
eret
+ b 2f
1:
/*
@@ -228,6 +229,7 @@
msr spsr_el3, \tmp
msr elr_el3, \ep
eret
+2:
.endm
/*
--- a/arch/arm/cpu/armv8/transition.S
+++ b/arch/arm/cpu/armv8/transition.S
@@ -36,8 +36,46 @@
* address saved in x4.
*/
br x4
-1: armv8_switch_to_el2_m x4, x5, x6
+1:
+
+ adr x8, msg_before
+ bl uart5_asciiz
+
+ adr x8, switch_to_el2_ok
+ armv8_switch_to_el2_m x8, x5, x6
+
+ adr x8, msg_aft_ko
+ bl uart5_asciiz
+
+switch_to_el2_ko:
+ b switch_to_el2_ko
+
+switch_to_el2_ok:
+ adr x8, msg_aft_ok
+ bl uart5_asciiz
+
+ br x4
+
+msg_before: .asciz "before switch from EL3 to EL2\n"
+msg_aft_ko: .asciz "switch to EL2 failed\n"
+msg_aft_ok: .asciz "now running in EL2\n"
ENDPROC(armv8_switch_to_el2)
+
+ENTRY(uart5_asciiz)
+ mov x10, #0x8000
+ movk x10, #0xFF17, lsl #16
+2:
+ ldrb w9, [x8]
+ cbnz w9, 3f
+ ret
+3:
+ add x8, x8, #1
+4:
+ ldr w11, [x10, #20] // [UART5_LSR]
+ tbz w11, #5, 4b // while (!trans_hold_reg_empty)
+ str w9, [x10] // [UART5_THR] <= *str++;
+ b 2b
+ENDPROC(uart5_asciiz)
.popsection
.pushsection .text.armv8_switch_to_el1, "ax"
