arm: mediatek: add support for MediaTek MT7987 SoC
This patch adds basic support for MediaTek MT7987 SoC.
This includes files that will initialize the SoC after boot and
its device tree.
In order to maximize the continuous usable memory space, MT7987 has its
ATF BL31 loaded at the top of RAM. Since u-boot will also locate itself to
top of RAM, u-boot will read the actual memory region of BL31 and set
correct gd->ram_top to avoid u-boot overlapping with BL31.
As now support for mt7987 hasn't been submitted to linux kernel, all dts
filed will be put to arch/arm/dts. They'll be removed after successfully
being merged by linux kernel, and OF_UPSTREAM will also be switched on.
diff --git a/arch/arm/mach-mediatek/mt7987/lowlevel_init.S b/arch/arm/mach-mediatek/mt7987/lowlevel_init.S
new file mode 100644
index 0000000..2f97255
--- /dev/null
+++ b/arch/arm/mach-mediatek/mt7987/lowlevel_init.S
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2023 MediaTek Inc.
+ * Author: Sam Shih <sam.shih@mediatek.com>
+ */
+
+/*
+ * Switch from AArch64 EL2 to AArch32 EL2
+ * @param inputs:
+ * x0: argument, zero
+ * x1: machine nr
+ * x2: fdt address
+ * x3: input argument
+ * x4: kernel entry point
+ * @param outputs for secure firmware:
+ * x0: function id
+ * x1: kernel entry point
+ * x2: machine nr
+ * x3: fdt address
+*/
+
+.global armv8_el2_to_aarch32
+armv8_el2_to_aarch32:
+ mov x3, x2
+ mov x2, x1
+ mov x1, x4
+ mov x4, #0
+ ldr x0, =0x82000200
+ SMC #0
+ ret