riscv: Fix builtin DTB handling

All SiPeed K210 MAIX boards have the exact same vendor, arch and
implementation IDs, preventing differentiation to select the correct
device tree to use through the SOC_BUILTIN_DTB_DECLARE() macro. This
result in this macro to be useless and mandates changing the code of
the sysctl driver to change the builtin device tree suitable for the
target board.

Fix this problem by removing the SOC_BUILTIN_DTB_DECLARE() macro since
it is used only for the K210 support. The code searching the builtin
DTBs using the vendor, arch an implementation IDs is also removed.
Support for builtin DTB falls back to the simpler and more traditional
handling of builtin DTB using the CONFIG_BUILTIN_DTB option, similarly
to other architectures.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

6 files changed, 19 insertions, 78 deletions

diff --git a/arch/riscv/Kconfig.socs b/arch/riscv/Kconfig.socs
index 3284d5c291be..59000675cb9f 100644
--- a/arch/riscv/Kconfig.socs
+++ b/arch/riscv/Kconfig.socs
@@ -32,9 +32,7 @@ config SOC_KENDRYTE
 	help
 	  This enables support for Kendryte K210 SoC platform hardware.
 
-config SOC_KENDRYTE_K210_DTB
-	def_bool y
-	depends on SOC_KENDRYTE_K210_DTB_BUILTIN
+if SOC_KENDRYTE
 
 config SOC_KENDRYTE_K210_DTB_BUILTIN
 	bool "Builtin device tree for the Kendryte K210"
@@ -42,10 +40,21 @@ config SOC_KENDRYTE_K210_DTB_BUILTIN
 	default y
 	select OF
 	select BUILTIN_DTB
-	select SOC_KENDRYTE_K210_DTB
 	help
-	  Builds a device tree for the Kendryte K210 into the Linux image.
+	  Build a device tree for the Kendryte K210 into the Linux image.
 	  This option should be selected if no bootloader is being used.
 	  If unsure, say Y.
 
+config SOC_KENDRYTE_K210_DTB_SOURCE
+	string "Source file for the Kendryte K210 builtin DTB"
+	depends on SOC_KENDRYTE
+	depends on SOC_KENDRYTE_K210_DTB_BUILTIN
+	default "k210"
+	help
+	  Base name (without suffix, relative to arch/riscv/boot/dts/kendryte)
+	  for the DTS file that will be used to produce the DTB linked into the
+	  kernel.
+
+endif
+
 endmenu
diff --git a/arch/riscv/boot/dts/Makefile b/arch/riscv/boot/dts/Makefile
index ca1f8cbd78c0..21e3905f1c44 100644
--- a/arch/riscv/boot/dts/Makefile
+++ b/arch/riscv/boot/dts/Makefile
@@ -1,5 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
 subdir-y += sifive
-subdir-y += kendryte
+subdir-$(CONFIG_SOC_KENDRYTE) += kendryte
 
 obj-$(CONFIG_BUILTIN_DTB) := $(addsuffix /, $(subdir-y))
diff --git a/arch/riscv/boot/dts/kendryte/Makefile b/arch/riscv/boot/dts/kendryte/Makefile
index 1a88e616f18e..83636693166d 100644
--- a/arch/riscv/boot/dts/kendryte/Makefile
+++ b/arch/riscv/boot/dts/kendryte/Makefile
@@ -1,4 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
-dtb-$(CONFIG_SOC_KENDRYTE_K210_DTB) += k210.dtb
-
+ifneq ($(CONFIG_SOC_KENDRYTE_K210_DTB_SOURCE),"")
+dtb-y += $(strip $(shell echo $(CONFIG_SOC_KENDRYTE_K210_DTB_SOURCE))).dtb
 obj-$(CONFIG_SOC_KENDRYTE_K210_DTB_BUILTIN) += $(addsuffix .o, $(dtb-y))
+endif
diff --git a/arch/riscv/include/asm/soc.h b/arch/riscv/include/asm/soc.h
index 6c8363b1f327..f494066051a2 100644
--- a/arch/riscv/include/asm/soc.h
+++ b/arch/riscv/include/asm/soc.h
@@ -21,42 +21,4 @@ void soc_early_init(void);
 extern unsigned long __soc_early_init_table_start;
 extern unsigned long __soc_early_init_table_end;
 
-/*
- * Allows Linux to provide a device tree, which is necessary for SOCs that
- * don't provide a useful one on their own.
- */
-struct soc_builtin_dtb {
-	unsigned long vendor_id;
-	unsigned long arch_id;
-	unsigned long imp_id;
-	void *(*dtb_func)(void);
-};
-
-/*
- * The argument name must specify a valid DTS file name without the dts
- * extension.
- */
-#define SOC_BUILTIN_DTB_DECLARE(name, vendor, arch, impl)		\
-	extern void *__dtb_##name##_begin;				\
-									\
-	static __init __used						\
-	void *__soc_builtin_dtb_f__##name(void)				\
-	{								\
-		return (void *)&__dtb_##name##_begin;			\
-	}								\
-									\
-	static const struct soc_builtin_dtb __soc_builtin_dtb__##name	\
-		__used __section("__soc_builtin_dtb_table") =		\
-	{								\
-		.vendor_id = vendor,					\
-		.arch_id   = arch,					\
-		.imp_id    = impl,					\
-		.dtb_func  = __soc_builtin_dtb_f__##name,		\
-	}
-
-extern unsigned long __soc_builtin_dtb_table_start;
-extern unsigned long __soc_builtin_dtb_table_end;
-
-void *soc_lookup_builtin_dtb(void);
-
 #endif
diff --git a/arch/riscv/kernel/soc.c b/arch/riscv/kernel/soc.c
index c7b0a73e382e..a0516172a33c 100644
--- a/arch/riscv/kernel/soc.c
+++ b/arch/riscv/kernel/soc.c
@@ -26,30 +26,3 @@ void __init soc_early_init(void)
 		}
 	}
 }
-
-static bool soc_builtin_dtb_match(unsigned long vendor_id,
-				unsigned long arch_id, unsigned long imp_id,
-				const struct soc_builtin_dtb *entry)
-{
-	return entry->vendor_id == vendor_id &&
-	       entry->arch_id == arch_id &&
-	       entry->imp_id == imp_id;
-}
-
-void * __init soc_lookup_builtin_dtb(void)
-{
-	unsigned long vendor_id, arch_id, imp_id;
-	const struct soc_builtin_dtb *s;
-
-	__asm__ ("csrr %0, mvendorid" : "=r"(vendor_id));
-	__asm__ ("csrr %0, marchid" : "=r"(arch_id));
-	__asm__ ("csrr %0, mimpid" : "=r"(imp_id));
-
-	for (s = (void *)&__soc_builtin_dtb_table_start;
-	     (void *)s < (void *)&__soc_builtin_dtb_table_end; s++) {
-		if (soc_builtin_dtb_match(vendor_id, arch_id, imp_id, s))
-			return s->dtb_func();
-	}
-
-	return NULL;
-}
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index bf5379135e39..77bd23f47a72 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -605,11 +605,7 @@ static void __init setup_vm_final(void)
 asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 {
 #ifdef CONFIG_BUILTIN_DTB
-	dtb_early_va = soc_lookup_builtin_dtb();
-	if (!dtb_early_va) {
-		/* Fallback to first available DTS */
-		dtb_early_va = (void *) __dtb_start;
-	}
+	dtb_early_va = (void *) __dtb_start;
 #else
 	dtb_early_va = (void *)dtb_pa;
 #endif