riscv: Fix builtin DTB handling

All SiPeed K210 boards have the exact same vendor, arch and
implementation IDs, preventing differentiation of the device tree to use
through the SOC_BUILTIN_DTB_DECLARE() macro. This result in this macro,
used only for Kendryte, to be useless and to prevent changing the
builtin device tree without also changing the code of the sysctl soc
driver.

Fix this problem by removing the SOC_BUILTIN_DTB_DECLARE() macro and
associated code, falling back to a simpler, and more traditional
handling of builtin DTB similar to other architectures.

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

arch/riscv/Kconfig.socs

@@ -33,20 +33,32 @@ 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
+config BUILTIN_DTB
+	def_bool n
+
+if SOC_KENDRYTE
 
 config SOC_KENDRYTE_K210_DTB_BUILTIN
 	bool "Builtin device tree for the Kendryte K210"
 	depends on SOC_KENDRYTE
 	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

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

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

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;
-}

arch/riscv/mm/init.c

@@ -591,11 +591,7 @@ 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

drivers/soc/kendryte/k210-sysctl.c

@@ -246,15 +246,3 @@ static void __init k210_soc_early_init(const void *fdt)
 	iounmap(regs);
 }
 SOC_EARLY_INIT_DECLARE(generic_k210, "kendryte,k210", k210_soc_early_init);
-
-#ifdef CONFIG_SOC_KENDRYTE_K210_DTB_BUILTIN
-/*
- * Generic entry for the default k210.dtb embedded DTB for boards with:
- *   - Vendor ID: 0x4B5
- *   - Arch ID: 0xE59889E6A5A04149 (= "Canaan AI" in UTF-8 encoded Chinese)
- *   - Impl ID:	0x4D41495832303030 (= "MAIX2000")
- * These values are reported by the SiPEED MAXDUINO, SiPEED MAIX GO and
- * SiPEED Dan dock boards.
- */
-SOC_BUILTIN_DTB_DECLARE(k210, 0x4B5, 0xE59889E6A5A04149, 0x4D41495832303030);
-#endif