amlogic: axg: Add a build flag when using ATOS as BL32

BL2 is unconditionally setting 0 (OPTEE_AARCH64) in arg0 even when the
BL32 image is 32bit (OPTEE_AARCH32). This is causing the boot to hang
when ATOS (32bit Amlogic BL32 binary-only TEE OS) is used.

Since we are not aware of any Amlogic platform shipping a 64bit version
of ATOS we can hardcode OPTEE_AARCH32 / MODE_RW_32 when using ATOS.
Signed-off-by: Carlo Caione <ccaione@baylibre.com>
Change-Id: Iaea47cf6dc48bf8a646056761f02fb81b41c78a3

docs/plat/meson-axg.rst

@@ -18,6 +18,7 @@ In order to build it:
 .. code:: shell
 
     CROSS_COMPILE=aarch64-none-elf- make DEBUG=1 PLAT=axg [SPD=opteed]
+         [AML_USE_ATOS=1 when using ATOS as BL32]
 
 This port has been tested on a A113D board. After building it, follow the
 instructions in the `U-Boot repository`_, replacing the mentioned **bl31.img**

plat/amlogic/axg/axg_bl31_setup.c

@@ -84,6 +84,17 @@ void bl31_early_platform_setup2(u_register_t arg0, u_register_t arg1,
 	bl32_image_ep_info = *from_bl2->bl32_ep_info;
 	bl33_image_ep_info = *from_bl2->bl33_ep_info;
 
+#if AML_USE_ATOS
+	/*
+	 * BL2 is unconditionally setting 0 (OPTEE_AARCH64) in arg0 even when
+	 * the BL32 image is 32bit (OPTEE_AARCH32). This is causing the boot to
+	 * hang when ATOS (32bit Amlogic BL32 binary-only TEE OS) is used.
+	 *
+	 * Hardcode to OPTEE_AARCH32 / MODE_RW_32.
+	 */
+	bl32_image_ep_info.args.arg0 = MODE_RW_32;
+#endif
+
 	if (bl33_image_ep_info.pc == 0U) {
 		ERROR("BL31: BL33 entrypoint not obtained from BL2\n");
 		panic();

plat/amlogic/axg/platform.mk

@@ -66,6 +66,10 @@ SEPARATE_CODE_AND_RODATA	:= 1
 # Use Coherent memory
 USE_COHERENT_MEM		:= 1
 
+AML_USE_ATOS			:= 0
+$(eval $(call assert_boolean,AML_USE_ATOS))
+$(eval $(call add_define,AML_USE_ATOS))
+
 # Verify build config
 # -------------------