Date:   Tue, 21 Apr 2020 13:08:30 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     Atish Patra <Atish.Patra@....com>
CC:     linux-kernel@...r.kernel.org, Atish Patra <Atish.Patra@....com>,
        ardb@...nel.org, linux-efi@...r.kernel.org,
        linux-riscv@...ts.infradead.org, masahiroy@...nel.org,
        xypron.glpk@....de
Subject:     Re: [v4 PATCH 3/3] RISC-V: Add EFI stub support.

On Mon, 20 Apr 2020 20:33:36 PDT (-0700), Atish Patra wrote:
> Add a RISC-V architecture specific stub code that actually copies the
> actual kernel image to a valid address and jump to it after boot services
> are terminated. Enable UEFI related kernel configs as well for RISC-V.
>
> Signed-off-by: Atish Patra <atish.patra@....com>
> ---
>  arch/riscv/Kconfig                        |  20 ++++
>  arch/riscv/Makefile                       |   1 +
>  arch/riscv/configs/defconfig              |   1 +
>  arch/riscv/include/asm/efi.h              |  44 +++++++++
>  drivers/firmware/efi/Kconfig              |   2 +-
>  drivers/firmware/efi/libstub/Makefile     |  10 ++
>  drivers/firmware/efi/libstub/riscv-stub.c | 106 ++++++++++++++++++++++
>  7 files changed, 183 insertions(+), 1 deletion(-)
>  create mode 100644 arch/riscv/include/asm/efi.h
>  create mode 100644 drivers/firmware/efi/libstub/riscv-stub.c
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index f39e326a7a42..eb4f41c8f3ce 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -379,10 +379,30 @@ 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_STUB

So I guess just "select RISCV_ISA_C" would be sufficient to make this work, but
I still feel flike an explicit "c.li" is saner.

> +	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 fb6e37db836d..079435804d6d 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -80,6 +80,7 @@ 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 4da4886246a4..ae69e12d306a 100644
> --- a/arch/riscv/configs/defconfig
> +++ b/arch/riscv/configs/defconfig
> @@ -129,3 +129,4 @@ CONFIG_DEBUG_BLOCK_EXT_DEVT=y
>  # CONFIG_RUNTIME_TESTING_MENU is not set
>  CONFIG_MEMTEST=y
>  # CONFIG_SYSFS_SYSCALL is not set
> +CONFIG_EFI=y
> diff --git a/arch/riscv/include/asm/efi.h b/arch/riscv/include/asm/efi.h
> new file mode 100644
> index 000000000000..62d7d5eafed8
> --- /dev/null
> +++ b/arch/riscv/include/asm/efi.h
> @@ -0,0 +1,44 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2020 Western Digital Corporation or its affiliates.
> + * Based on arch/arm64/include/asm/efi.h
> + */
> +#ifndef _ASM_EFI_H
> +#define _ASM_EFI_H
> +
> +#include <asm/io.h>
> +#include <asm/mmu_context.h>
> +#include <asm/ptrace.h>
> +#include <asm/tlbflush.h>
> +
> +#define VA_BITS_MIN 39

I don't see this actually being used, but if it's releant to some macro that
I'm missing then EFI support should depend on rv64.

> +
> +/* on RISC-V, the FDT may be located anywhere in system RAM */
> +static inline unsigned long efi_get_max_fdt_addr(unsigned long dram_base)
> +{
> +	return ULONG_MAX;
> +}
> +
> +/* Load initrd at enough distance from DRAM start */
> +static inline unsigned long efi_get_max_initrd_addr(unsigned long dram_base,
> +						    unsigned long image_addr)
> +{
> +	return dram_base + SZ_256M;
> +}
> +
> +#define efi_bs_call(func, ...)	efi_system_table()->boottime->func(__VA_ARGS__)
> +#define efi_rt_call(func, ...)	efi_system_table()->runtime->func(__VA_ARGS__)
> +#define efi_is_native()		(true)
> +
> +#define efi_table_attr(inst, attr)	(inst->attr)
> +
> +#define efi_call_proto(inst, func, ...) inst->func(inst, ##__VA_ARGS__)
> +
> +#define alloc_screen_info(x...)		(&screen_info)
> +extern char stext_offset[];
> +
> +static inline void free_screen_info(struct screen_info *si)
> +{
> +}
> +
> +#endif /* _ASM_EFI_H */
> diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
> index 2a2b2b96a1dc..fcdc789d3f87 100644
> --- a/drivers/firmware/efi/Kconfig
> +++ b/drivers/firmware/efi/Kconfig
> @@ -111,7 +111,7 @@ config EFI_GENERIC_STUB
>
>  config EFI_ARMSTUB_DTB_LOADER
>  	bool "Enable the DTB loader"
> -	depends on EFI_GENERIC_STUB
> +	depends on EFI_GENERIC_STUB && !RISCV
>  	default y
>  	help
>  	  Select this config option to add support for the dtb= command
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index 0f57293d777e..eb365c55c0fe 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -22,6 +22,8 @@ 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-$(CONFIG_EFI_GENERIC_STUB) += -I$(srctree)/scripts/dtc/libfdt
>
> @@ -57,6 +59,7 @@ lib-$(CONFIG_EFI_GENERIC_STUB)	+= efi-stub.o fdt.o string.o \
>  lib-$(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=$(TEXT_OFFSET)
>
> @@ -100,6 +103,13 @@ STUBCOPY_FLAGS-$(CONFIG_X86)	+= --rename-section .bss=.bss.efistub,load,alloc
>  STUBCOPY_RELOC-$(CONFIG_X86_32)	:= R_386_32
>  STUBCOPY_RELOC-$(CONFIG_X86_64)	:= R_X86_64_64
>
> +# For RISC-V, we don't need anything special other than arm64. Keep all the
> +# symbols in .init section and make sure that no absolute symbols references
> +# doesn't exist.
> +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..bd1d6fed8754
> --- /dev/null
> +++ b/drivers/firmware/efi/libstub/riscv-stub.c
> @@ -0,0 +1,106 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2013, 2014 Linaro Ltd;  <roy.franz@...aro.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"
> +/*
> + * RISC-V requires the kernel image to placed 2 MB aligned base for 64 bit and
> + * 4MB for 32 bit.
> + */
> +#ifdef CONFIG_64BIT
> +#define MIN_KIMG_ALIGN	SZ_2M
> +#else
> +#define MIN_KIMG_ALIGN	SZ_4M
> +#endif
> +
> +typedef __attribute__((noreturn)) void (*jump_kernel_func)(unsigned int,
> +							   unsigned long);
> +efi_status_t check_platform_features(void)
> +{
> +	return EFI_SUCCESS;
> +}
> +
> +static u32 get_boot_hartid_from_fdt(unsigned long fdt)
> +{
> +	int chosen_node, len;
> +	const fdt32_t *prop;
> +
> +	chosen_node = fdt_path_offset((void *)fdt, "/chosen");
> +	if (chosen_node < 0)
> +		return U32_MAX;
> +	prop = fdt_getprop((void *)fdt, chosen_node, "boot-hartid", &len);
> +	if (!prop || len != sizeof(u32))
> +		return U32_MAX;
> +
> +	return fdt32_to_cpu(*prop);
> +}
> +
> +/*
> + * 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 fdt_size)
> +{
> +	unsigned long kernel_entry = entrypoint + (unsigned long)stext_offset;
> +	jump_kernel_func jump_kernel = (jump_kernel_func) kernel_entry;
> +	u32 hartid = get_boot_hartid_from_fdt(fdt);
> +
> +	if (hartid == U32_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 = 0;
> +	unsigned long preferred_addr;
> +
> +	kernel_size = _edata - _start;
> +	*reserve_size = kernel_size + (_end - _edata);
> +	*image_addr = (unsigned long)_start;
> +
> +	/*
> +	 * RISC-V kernel maps PAGE_OFFSET virtual address to the same physical
> +	 * address where kernel is booted. That's why kernel should boot from
> +	 * as low as possible to avoid wastage of memory. Currently, dram_base
> +	 * is occupied by the firmware. So the preferred address for kernel to
> +	 * boot is next aligned address. If preferred address is not available,
> +	 * relocate_kernel will fall back to efi_low_alloc_above to allocate
> +	 * lowest possible memory region as long as the address and size meets
> +	 * the alignment constraints.
> +	 */
> +	preferred_addr = round_up(dram_base, MIN_KIMG_ALIGN) + MIN_KIMG_ALIGN;
> +	status = efi_relocate_kernel(image_addr, kernel_size, *reserve_size,
> +				     preferred_addr, MIN_KIMG_ALIGN, dram_base);
> +
> +	if (status != EFI_SUCCESS) {
> +		pr_efi_err("Failed to relocate kernel\n");
> +		*reserve_size = 0;
> +		return status;
> +	}
> +
> +	return EFI_SUCCESS;
> +}

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