armv8: fsl-layerscape: Support loading 32-bit OS with PSCI enabled

As PSCI and secure monitor firmware framework are enabled, this patch is
to support loading 32-bit OS in such case. The default target exception
level returned to U-Boot is EL2, so the corresponding work to switch to
AArch32 EL2 and jump to 32-bit OS are done in U-Boot and secure firmware
together.

Signed-off-by: Alison Wang <alison.wang@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>

arch/arm/cpu/armv8/sec_firmware_asm.S

@@ -50,4 +50,27 @@ ENTRY(_sec_firmware_support_psci_version)
 	smc	#0
 	ret
 ENDPROC(_sec_firmware_support_psci_version)
+
+/*
+ * Switch from AArch64 EL2 to AArch32 EL2
+ * @param inputs:
+ * x0: argument, zero
+ * x1: machine nr
+ * x2: fdt address
+ * x3: kernel entry point
+ * @param outputs for secure firmware:
+ * x0: function id
+ * x1: kernel entry point
+ * x2: machine nr
+ * x3: fdt address
+*/
+ENTRY(armv8_el2_to_aarch32)
+	mov	x0, x3
+	mov	x3, x2
+	mov	x2, x1
+	mov	x1, x0
+	ldr	x0, =0xc000ff04
+	smc	#0
+	ret
+ENDPROC(armv8_el2_to_aarch32)
 #endif

arch/arm/cpu/armv8/transition.S

@@ -13,6 +13,14 @@
 ENTRY(armv8_switch_to_el2)
 	switch_el x5, 1f, 0f, 0f
 0:
+	cmp x4, #ES_TO_AARCH64
+	b.eq 2f
+	/*
+	 * When loading 32-bit kernel, it will jump
+	 * to secure firmware again, and never return.
+	 */
+	bl armv8_el2_to_aarch32
+2:
 	/*
 	 * x3 is kernel entry point or switch_to_el1
 	 * if CONFIG_ARMV8_SWITCH_TO_EL1 is defined.
@@ -32,3 +40,7 @@ ENTRY(armv8_switch_to_el1)
 	br x3
 1:	armv8_switch_to_el1_m x3, x4, x5
 ENDPROC(armv8_switch_to_el1)
+
+WEAK(armv8_el2_to_aarch32)
+	ret
+ENDPROC(armv8_el2_to_aarch32)

arch/arm/include/asm/system.h

@@ -215,6 +215,8 @@ void armv8_switch_to_el2(u64 args, u64 mach_nr, u64 fdt_addr,
  */
 void armv8_switch_to_el1(u64 args, u64 mach_nr, u64 fdt_addr,
 			 u64 entry_point, u64 es_flag);
+void armv8_el2_to_aarch32(u64 args, u64 mach_nr, u64 fdt_addr,
+			  u64 entry_point);
 void gic_init(void);
 void gic_send_sgi(unsigned long sgino);
 void wait_for_wakeup(void);