[PATCH v2 1/3] riscv: obtain ACPI RSDP from FFI.

[Yunhui Cui]

1. We need to enable the ACPI function on RISC-V. When booting with
Coreboot, we encounter two problems:
a. Coreboot does not support EFI
b. On RISC-V, only the DTS channel can be used.

2. Based on this, we have added an interface for obtaining firmware
information transfer through FDT, named FFI.

3. We not only use FFI to pass ACPI RSDP, but also pass other
firmware information as an extension.

Signed-off-by: Yunhui Cui <cuiyunhui at bytedance.com>
---
 MAINTAINERS                   |  6 ++++++
 arch/riscv/Kconfig            | 10 ++++++++++
 arch/riscv/include/asm/acpi.h |  9 +++++++++
 arch/riscv/include/asm/ffi.h  |  9 +++++++++
 arch/riscv/kernel/Makefile    |  1 +
 arch/riscv/kernel/ffi.c       | 37 +++++++++++++++++++++++++++++++++++
 arch/riscv/kernel/setup.c     |  2 ++
 7 files changed, 74 insertions(+)
 create mode 100644 arch/riscv/include/asm/ffi.h
 create mode 100644 arch/riscv/kernel/ffi.c

diff --git a/MAINTAINERS b/MAINTAINERS
index cd5388a33410..e592f489e757 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -18363,6 +18363,12 @@ F:	arch/riscv/boot/dts/
 X:	arch/riscv/boot/dts/allwinner/
 X:	arch/riscv/boot/dts/renesas/
 
+RISC-V FDT FIRMWARE INTERFACE (FFI) SUPPORT
+M:	Yunhui Cui cuiyunhui at bytedance.com
+S:	Maintained
+F:	arch/riscv/include/asm/ffi.h
+F:	arch/riscv/kernel/ffi.c
+
 RISC-V PMU DRIVERS
 M:	Atish Patra <atishp at atishpatra.org>
 R:	Anup Patel <anup at brainfault.org>
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index b49793cf34eb..2e1c40fb2300 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -785,6 +785,16 @@ config EFI
 	  allow the kernel to be booted as an EFI application. This
 	  is only useful on systems that have UEFI firmware.
 
+config FFI
+	bool "Fdt firmware interface"
+	depends on OF
+	default y
+	help
+	  Added an interface to obtain firmware information transfer
+	  through FDT, named FFI. Some bootloaders do not support EFI,
+	  such as coreboot.
+	  We can pass firmware information through FFI, such as ACPI.
+
 config CC_HAVE_STACKPROTECTOR_TLS
 	def_bool $(cc-option,-mstack-protector-guard=tls -mstack-protector-guard-reg=tp -mstack-protector-guard-offset=0)
 
diff --git a/arch/riscv/include/asm/acpi.h b/arch/riscv/include/asm/acpi.h
index f71ce21ff684..f9d1625dd159 100644
--- a/arch/riscv/include/asm/acpi.h
+++ b/arch/riscv/include/asm/acpi.h
@@ -15,6 +15,8 @@
 /* Basic configuration for ACPI */
 #ifdef CONFIG_ACPI
 
+#include <asm/ffi.h>
+
 typedef u64 phys_cpuid_t;
 #define PHYS_CPUID_INVALID INVALID_HARTID
 
@@ -66,6 +68,13 @@ int acpi_get_riscv_isa(struct acpi_table_header *table,
 		       unsigned int cpu, const char **isa);
 
 static inline int acpi_numa_get_nid(unsigned int cpu) { return NUMA_NO_NODE; }
+
+#define ACPI_HAVE_ARCH_GET_ROOT_POINTER
+static inline u64 acpi_arch_get_root_pointer(void)
+{
+	return acpi_rsdp;
+}
+
 #else
 static inline void acpi_init_rintc_map(void) { }
 static inline struct acpi_madt_rintc *acpi_cpu_get_madt_rintc(int cpu)
diff --git a/arch/riscv/include/asm/ffi.h b/arch/riscv/include/asm/ffi.h
new file mode 100644
index 000000000000..847af02abd87
--- /dev/null
+++ b/arch/riscv/include/asm/ffi.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _ASM_FFI_H
+#define _ASM_FFI_H
+
+extern u64 acpi_rsdp;
+extern void ffi_init(void);
+
+#endif /* _ASM_FFI_H */
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 506cc4a9a45a..274e06f4da33 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -92,6 +92,7 @@ obj-$(CONFIG_CRASH_CORE)	+= crash_core.o
 obj-$(CONFIG_JUMP_LABEL)	+= jump_label.o
 
 obj-$(CONFIG_EFI)		+= efi.o
+obj-$(CONFIG_FFI)              += ffi.o
 obj-$(CONFIG_COMPAT)		+= compat_syscall_table.o
 obj-$(CONFIG_COMPAT)		+= compat_signal.o
 obj-$(CONFIG_COMPAT)		+= compat_vdso/
diff --git a/arch/riscv/kernel/ffi.c b/arch/riscv/kernel/ffi.c
new file mode 100644
index 000000000000..c5ac2b5d9148
--- /dev/null
+++ b/arch/riscv/kernel/ffi.c
@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * ffi.c - FDT FIRMWARE INTERFACE
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/of.h>
+#include <linux/of_fdt.h>
+#include <linux/libfdt.h>
+
+u64 acpi_rsdp;
+
+void __init ffi_acpi_root_pointer(void)
+{
+	int cfgtbl, len;
+	fdt64_t *prop;
+
+	cfgtbl = fdt_path_offset(initial_boot_params, "/cfgtables");
+	if (cfgtbl < 0) {
+		pr_info("firmware table not found.\n");
+		return;
+	}
+
+	prop = fdt_getprop_w(initial_boot_params, cfgtbl, "acpi_phy_ptr", &len);
+	if (!prop || len != sizeof(u64))
+		pr_info("acpi_rsdp not found.\n");
+	else
+		acpi_rsdp = fdt64_to_cpu(*prop);
+
+	pr_debug("acpi rsdp: %llx\n", acpi_rsdp);
+}
+
+void __init ffi_init(void)
+{
+	ffi_acpi_root_pointer();
+}
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index 971fe776e2f8..5a933d6b6acb 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -36,6 +36,7 @@
 #include <asm/thread_info.h>
 #include <asm/kasan.h>
 #include <asm/efi.h>
+#include <asm/ffi.h>
 
 #include "head.h"
 
@@ -279,6 +280,7 @@ void __init setup_arch(char **cmdline_p)
 	parse_early_param();
 
 	efi_init();
+	ffi_init();
 	paging_init();
 
 	/* Parse the ACPI tables for possible boot-time configuration */
-- 
2.20.1