[RFC,5/5] RISC-V: Add EFI stub support.

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 42c122170cfd..68b1d565e51d 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -372,10 +372,30 @@  config CMDLINE_FORCE
 
 endchoice
 
+config EFI_STUB
+	bool
+
+config EFI
+	bool "UEFI runtime support"
+	depends on OF
+	select LIBFDT
+	select UCS2_STRING
+	select EFI_PARAMS_FROM_FDT
+	select EFI_STUB
+	select EFI_GENERIC_ARCH_STUB
+	default y
+	help
+	  This option provides support for runtime services provided
+	  by UEFI firmware (such as non-volatile variables, realtime
+          clock, and platform reset). A UEFI stub is also provided to
+	  allow the kernel to be booted as an EFI application. This
+	  is only useful on systems that have UEFI firmware.
+
 endmenu
 
 menu "Power management options"
 
 source "kernel/power/Kconfig"
+source "drivers/firmware/Kconfig"
 
 endmenu
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index b9009a2fbaf5..0afaa89ba9ad 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -78,6 +78,7 @@  head-y := arch/riscv/kernel/head.o
 core-y += arch/riscv/
 
 libs-y += arch/riscv/lib/
+core-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
 
 PHONY += vdso_install
 vdso_install:
diff --git a/arch/riscv/configs/defconfig b/arch/riscv/configs/defconfig
index e2ff95cb3390..0a5d3578f51e 100644
--- a/arch/riscv/configs/defconfig
+++ b/arch/riscv/configs/defconfig
@@ -125,3 +125,4 @@  CONFIG_DEBUG_BLOCK_EXT_DEVT=y
 # CONFIG_FTRACE is not set
 # CONFIG_RUNTIME_TESTING_MENU is not set
 CONFIG_MEMTEST=y
+CONFIG_EFI=y
diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index 2c5b76787126..38facb61745b 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -21,6 +21,8 @@  cflags-$(CONFIG_ARM64)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
 cflags-$(CONFIG_ARM)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
 				   -fno-builtin -fpic \
 				   $(call cc-option,-mno-single-pic-base)
+cflags-$(CONFIG_RISCV)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
+				   -fpic
 
 cflags-$(CONFIG_EFI_GENERIC_ARCH_STUB)	+= -I$(srctree)/scripts/dtc/libfdt
 
@@ -55,6 +57,7 @@  lib-$(CONFIG_EFI_GENERIC_ARCH_STUB)		+= efi-stub.o fdt.o string.o \
 lib-$(CONFIG_ARM)		+= arm32-stub.o
 lib-$(CONFIG_ARM64)		+= arm64-stub.o
 lib-$(CONFIG_X86)		+= x86-stub.o
+lib-$(CONFIG_RISCV)		+= riscv-stub.o
 CFLAGS_arm32-stub.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
 CFLAGS_arm64-stub.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
 
@@ -79,6 +82,11 @@  STUBCOPY_FLAGS-$(CONFIG_ARM64)	+= --prefix-alloc-sections=.init \
 				   --prefix-symbols=__efistub_
 STUBCOPY_RELOC-$(CONFIG_ARM64)	:= R_AARCH64_ABS
 
+STUBCOPY_FLAGS-$(CONFIG_RISCV)	+= --prefix-alloc-sections=.init \
+				   --prefix-symbols=__efistub_
+STUBCOPY_RELOC-$(CONFIG_RISCV)	:= R_RISCV_HI20
+
+
 $(obj)/%.stub.o: $(obj)/%.o FORCE
 	$(call if_changed,stubcopy)
 
diff --git a/drivers/firmware/efi/libstub/riscv-stub.c b/drivers/firmware/efi/libstub/riscv-stub.c
new file mode 100644
index 000000000000..3935b29ea93a
--- /dev/null
+++ b/drivers/firmware/efi/libstub/riscv-stub.c
@@ -0,0 +1,135 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2013, 2014 Linaro Ltd;  <roy.franz@linaro.org>
+ * Copyright (C) 2020 Western Digital Corporation or its affiliates.
+ *
+ * This file implements the EFI boot stub for the RISC-V kernel.
+ * Adapted from ARM64 version at drivers/firmware/efi/libstub/arm64-stub.c.
+ */
+
+#include <linux/efi.h>
+#include <linux/libfdt.h>
+#include <linux/libfdt_env.h>
+#include <asm/efi.h>
+#include <asm/sections.h>
+
+#include "efistub.h"
+/*
+ * RISCV requires the kernel image to placed TEXT_OFFSET bytes beyond a 2 MB
+ * aligned base for 64 bit and 4MB for 32 bit.
+ */
+#if IS_ENABLED(CONFIG_64BIT)
+#define MIN_KIMG_ALIGN	SZ_2M
+#else
+#define MIN_KIMG_ALIGN	SZ_4M
+#endif
+/*
+ * TEXT_OFFSET ensures that we don't overwrite the firmware that probably sits
+ * at the beginning of the DRAM.
+ */
+#define TEXT_OFFSET MIN_KIMG_ALIGN
+
+typedef __attribute__((noreturn)) void (*jump_kernel_func)(unsigned int,
+							   unsigned long);
+
+efi_status_t check_platform_features(void)
+{
+	return EFI_SUCCESS;
+}
+
+u64 get_boot_hartid_from_fdt(unsigned long fdt)
+{
+	int chosen_node, len;
+	const fdt64_t *prop;
+	uint64_t hartid = U64_MAX;
+
+	chosen_node = fdt_path_offset((void *)fdt, "/chosen");
+	if (chosen_node < 0)
+		return hartid;
+	prop = fdt_getprop((void *)fdt, chosen_node, "efi-boot-hartid", &len);
+	if (!prop || len != sizeof(u64))
+		return hartid;
+
+	hartid = fdt64_to_cpu(*prop);
+
+	return hartid;
+}
+
+/*
+ * Jump to real kernel here with following constraints.
+ * 1. MMU should be disabled.
+ * 2. a0 should contain hartid
+ * 3. a1 should DT address
+ */
+void __noreturn efi_enter_kernel(unsigned long entrypoint, unsigned long fdt)
+{
+	unsigned long kernel_entry = entrypoint + _start_kernel - _start;
+	jump_kernel_func jump_kernel = (void (*)(unsigned int, unsigned long))kernel_entry;
+	u64 hartid = get_boot_hartid_from_fdt(fdt);
+
+	if (hartid == U64_MAX)
+		/* We can not use panic or BUG at this point */
+		__asm__ __volatile__ ("ebreak");
+	/* Disable MMU */
+	csr_write(CSR_SATP, 0);
+	jump_kernel(hartid, fdt);
+}
+
+efi_status_t handle_kernel_image(unsigned long *image_addr,
+				 unsigned long *image_size,
+				 unsigned long *reserve_addr,
+				 unsigned long *reserve_size,
+				 unsigned long dram_base,
+				 efi_loaded_image_t *image)
+{
+	efi_status_t status;
+	unsigned long kernel_size, kernel_memsize = 0;
+	unsigned long preferred_offset;
+
+	/*
+	 * The preferred offset of the kernel Image is TEXT_OFFSET bytes beyond
+	 * a KIMG_ALIGN aligned base.
+	 */
+	preferred_offset = round_up(dram_base, MIN_KIMG_ALIGN) + TEXT_OFFSET;
+
+	kernel_size = _edata - _start;
+	kernel_memsize = kernel_size + (_end - _edata);
+
+	/*
+	 * Try a straight allocation at the preferred offset.
+	 * This will work around the issue where, if dram_base == 0x0,
+	 * efi_low_alloc() refuses to allocate at 0x0 (to prevent the
+	 * address of the allocation to be mistaken for a FAIL return
+	 * value or a NULL pointer). It will also ensure that, on
+	 * platforms where the [dram_base, dram_base + TEXT_OFFSET)
+	 * interval is partially occupied by the firmware (like on APM
+	 * Mustang), we can still place the kernel at the address
+	 * 'dram_base + TEXT_OFFSET'.
+	 */
+	if (*image_addr == preferred_offset)
+		return EFI_SUCCESS;
+
+	*image_addr = *reserve_addr = preferred_offset;
+	*reserve_size = round_up(kernel_memsize, EFI_ALLOC_ALIGN);
+
+	status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS,
+				EFI_LOADER_DATA,
+				*reserve_size / EFI_PAGE_SIZE,
+				(efi_physical_addr_t *)reserve_addr);
+
+	if (status != EFI_SUCCESS) {
+		*reserve_size = kernel_memsize + TEXT_OFFSET;
+		status = efi_low_alloc(*reserve_size, MIN_KIMG_ALIGN,
+				       reserve_addr);
+
+		if (status != EFI_SUCCESS) {
+			pr_efi_err("Failed to relocate kernel\n");
+			*reserve_size = 0;
+			return status;
+		}
+		*image_addr = *reserve_addr + TEXT_OFFSET;
+	}
+	memcpy((void *)*image_addr, image->image_base, kernel_size);
+
+	return EFI_SUCCESS;
+}