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arch: arm64: Enable config option to switch from EL3 to EL1

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ARMv8-A SoCs enter EL3 after reset. Add a new config option
(CONFIG_SWITCH_TO_EL1) to switch from EL3 to EL1 at boot and default it
to 'y'.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>
This commit is contained in:
Carlo Caione 2019-11-20 20:50:24 +00:00 • committed by Anas Nashif
commit 6531d1c649
2 changed files with 33 additions and 0 deletions
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7
arch/arm/core/aarch64/Kconfig
View file

@ -24,6 +24,13 @@ config CPU_CORTEX_A53
help
This option signifies the use of a Cortex-A53 CPU
config SWITCH_TO_EL1
bool "Switch to EL1 at boot"
default y
help
This option indicates that we want to switch to EL1 at boot. Only
switching to EL1 from EL3 is supported.
config NUM_IRQS
int

26
arch/arm/core/aarch64/reset.S
View file

@ -42,6 +42,32 @@ SECTION_SUBSEC_FUNC(TEXT,_reset_section,__reset)
GTEXT(__start)
SECTION_SUBSEC_FUNC(TEXT,_reset_section,__start)
#ifdef CONFIG_SWITCH_TO_EL1
switch_el x1, 3f, 2f, 1f
3:
/* Disable MMU and async exceptions routing to EL1 */
msr sctlr_el1, xzr
/* Disable EA/IRQ/FIQ routing to EL3 and set EL1 to AArch64 */
mov x0, xzr
orr x0, x0, #(SCR_EL3_RW)
msr scr_el3, x0
/* On eret return to EL1 with DAIF masked */
mov x0, xzr
orr x0, x0, #(DAIF_MASK)
orr x0, x0, #(SPSR_EL3_TO_EL1)
orr x0, x0, #(SPSR_EL3_h)
msr spsr_el3, x0
adr x0, 1f
msr elr_el3, x0
eret
2:
/* Boot from EL2 not supported */
bl .
1:
#endif
/* Setup vector table */
adr x0, _vector_table