RISC-V: Add kexec support

This patch adds support for kexec on RISC-V. On SMP systems it depends
on HOTPLUG_CPU in order to be able to bring up all harts after kexec.
It also needs a recent OpenSBI version that supports the HSM extension.
I tested it on riscv64 QEMU on both an smp and a non-smp system.

Signed-off-by: Nick Kossifidis <mick@ics.forth.gr>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/include/asm/kexec.h

@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2019 FORTH-ICS/CARV
+ *  Nick Kossifidis <mick@ics.forth.gr>
+ */
+
+#ifndef _RISCV_KEXEC_H
+#define _RISCV_KEXEC_H
+
+#include <asm/page.h>    /* For PAGE_SIZE */
+
+/* Maximum physical address we can use pages from */
+#define KEXEC_SOURCE_MEMORY_LIMIT (-1UL)
+
+/* Maximum address we can reach in physical address mode */
+#define KEXEC_DESTINATION_MEMORY_LIMIT (-1UL)
+
+/* Maximum address we can use for the control code buffer */
+#define KEXEC_CONTROL_MEMORY_LIMIT (-1UL)
+
+/* Reserve a page for the control code buffer */
+#define KEXEC_CONTROL_PAGE_SIZE PAGE_SIZE
+
+#define KEXEC_ARCH KEXEC_ARCH_RISCV
+
+static inline void
+crash_setup_regs(struct pt_regs *newregs,
+		 struct pt_regs *oldregs)
+{
+	/* Dummy implementation for now */
+}
+
+
+#define ARCH_HAS_KIMAGE_ARCH
+
+struct kimage_arch {
+	unsigned long fdt_addr;
+};
+
+const extern unsigned char riscv_kexec_relocate[];
+const extern unsigned int riscv_kexec_relocate_size;
+
+typedef void (*riscv_kexec_do_relocate)(unsigned long first_ind_entry,
+					unsigned long jump_addr,
+					unsigned long fdt_addr,
+					unsigned long hartid,
+					unsigned long va_pa_off);
+
+#endif