[PATCH v3 1/4] riscv: obtain ACPI RSDP from devicetree

[Yunhui Cui]

On RISC-V, Coreboot does not support booting using EFI, only devicetree
nor does RISC-V have a reserved address segment.
To allow using Coreboot on platforms that require ACPI, the ACPI RSDP
needs to be passed to supervisor mode software using devicetree.

Add support for parsing the "ffitbl" devicetree node to find the
ACPI entry point and use wire up acpi_arch_get_root_pointer().
This feature is known as FDT Firmware Interface (FFI).

Signed-off-by: Yunhui Cui <cuiyunhui at bytedance.com>
---
 MAINTAINERS                   |  6 ++++++
 arch/riscv/include/asm/acpi.h |  9 +++++++++
 arch/riscv/include/asm/ffi.h  | 14 +++++++++++++
 arch/riscv/kernel/Makefile    |  1 +
 arch/riscv/kernel/ffi.c       | 38 +++++++++++++++++++++++++++++++++++
 arch/riscv/kernel/setup.c     |  2 ++
 6 files changed, 70 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/include/asm/acpi.h b/arch/riscv/include/asm/acpi.h
index f71ce21ff684..5574f9a152f5 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 riscv_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..d5e8309cc06f
--- /dev/null
+++ b/arch/riscv/include/asm/ffi.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _ASM_FFI_H
+#define _ASM_FFI_H
+
+#ifdef CONFIG_FDT_FW_INTERFACE
+extern void ffi_init(void);
+extern u64 riscv_acpi_rsdp(void);
+#else
+#define ffi_init()
+static inline u64 riscv_acpi_rsdp(void) { return 0; }
+#endif
+
+#endif /* _ASM_FFI_H */
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 506cc4a9a45a..71831cf7f934 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_FDT_FW_INTERFACE)	+= 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..147d06a5acff
--- /dev/null
+++ b/arch/riscv/kernel/ffi.c
@@ -0,0 +1,38 @@
+// 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>
+
+static u64 acpi_rsdp;
+
+void __init ffi_acpi_root_pointer(void)
+{
+	u32 ffitbl, acpi, len;
+	fdt64_t *prop;
+
+	ffitbl = fdt_subnode_offset(initial_boot_params, 0, "ffitbl");
+	acpi = fdt_subnode_offset(initial_boot_params, ffitbl, "acpi");
+	prop = fdt_getprop_w(initial_boot_params, acpi, "entry", &len);
+	if (!prop || len != sizeof(u64)) {
+		pr_debug("acpi rsdp not found.\n");
+		return;
+	}
+	acpi_rsdp = fdt64_to_cpu(*prop);
+	pr_debug("acpi rsdp: %llx\n", acpi_rsdp);
+}
+
+u64 __init riscv_acpi_rsdp(void)
+{
+	return 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