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

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 <[email protected]>
yegorich · Feb 1, 2020 · 6531d1c · 6531d1c
1 parent 86a6047
commit 6531d1c
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diff --git a/arch/arm/core/aarch64/Kconfig b/arch/arm/core/aarch64/Kconfig
@@ -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
 

diff --git a/arch/arm/core/aarch64/reset.S b/arch/arm/core/aarch64/reset.S
@@ -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