riscv: Simplify payload handling

1. Simplify payload code and convert it to C
2. Save the FDT pointer to HLS (hart-local storage).
3. Don't use mscratch to pass FDT pointer as it is used for exception handling.

Change-Id: I32bf2a99e07a65358a7f19b899259f0816eb45e8
Signed-off-by: Xiang Wang <wxjstz@126.com>
Signed-off-by: Philipp Hug <philipp@hug.cx>
Reviewed-on: https://review.coreboot.org/c/31179
Reviewed-by: ron minnich <rminnich@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/arch/riscv/payload.c

@@ -0,0 +1,51 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright (C) 2016 Google Inc
+ * Copyright (C) 2018 HardenedLinux
+ * Copyright (C) 2018 Jonathan Neuschäfer
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <stdint.h>
+#include <arch/boot.h>
+#include <arch/encoding.h>
+#include <console/console.h>
+
+void run_payload(struct prog *prog, void *fdt, int payload_mode)
+{
+	void (*doit)(int hart_id, void *fdt) = prog_entry(prog);
+	int hart_id = read_csr(mhartid);
+	uintptr_t status = read_csr(mstatus);
+	status &= ~MSTATUS_MPIE;
+	status &= ~MSTATUS_MPP;
+	switch (payload_mode) {
+	case RISCV_PAYLOAD_MODE_U:
+		break;
+	case RISCV_PAYLOAD_MODE_S:
+		status |= MSTATUS_SPP;
+		break;
+	case RISCV_PAYLOAD_MODE_M:
+		doit(hart_id, fdt);
+		return;
+	default:
+		die("wrong privilege level for payload");
+		break;
+	}
+	write_csr(mstatus, status);
+	write_csr(mepc, doit);
+	asm volatile(
+		"mv a0, %0\n\t"
+		"mv a1, %0\n\t"
+		"mret" ::"r"(hart_id),
+		"r"(fdt)
+		: "a0", "a1");
+}