riscv: Save boot hart id to the global data

At present the hart id passed via a0 in the U-Boot entry is saved
to s0 at the beginning but does not preserve later. Save it to the
global data structure so that it can be used later.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: Anup Patel <anup@brainfault.org>

arch/riscv/cpu/start.S

@@ -14,6 +14,7 @@
 #include <common.h>
 #include <elf.h>
 #include <asm/encoding.h>
+#include <generated/asm-offsets.h>
 
 #ifdef CONFIG_32BIT
 #define LREG			lw
@@ -70,6 +71,9 @@ call_board_init_f_0:
 
 	jal	board_init_f_init_reserve
 
+	/* save the boot hart id to global_data */
+	SREG	s0, GD_BOOT_HART(gp)
+
 	mv	a0, zero		/* a0 <-- boot_flags = 0 */
 	la	t5, board_init_f
 	jr	t5			/* jump to board_init_f() */

arch/riscv/include/asm/global_data.h

@@ -12,6 +12,7 @@
 
 /* Architecture-specific global data */
 struct arch_global_data {
+	long boot_hart;		/* boot hart id */
 #ifdef CONFIG_SIFIVE_CLINT
 	void __iomem *clint;	/* clint base address */
 #endif

arch/riscv/lib/asm-offsets.c

@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2018, Bin Meng <bmeng.cn@gmail.com>
+ *
+ * From arch/x86/lib/asm-offsets.c
+ *
+ * This program is used to generate definitions needed by
+ * assembly language modules.
+ */
+
+#include <common.h>
+#include <linux/kbuild.h>
+
+int main(void)
+{
+	DEFINE(GD_BOOT_HART, offsetof(gd_t, arch.boot_hart));
+
+	return 0;
+}